TY - THES A1 - Alsarem, Mazen T1 - Semantic Snippets via Query-Biased Ranking of Linked Data Entities N2 - In our knowledge-driven society, the acquisition and the transfer of knowledge play a principal role. Web search engines are somehow tools for knowledge acquisition and transfer from the web to the user. The search engine results page (SERP) consists mainly of a list of links and snippets (excerpts from the results). The snippets are used to express, as efficiently as possible, the way a web page may be relevant to the query. As an extension of the existing web, the semantic web or “web 3.0” is designed to convert the presently available web of unstructured documents into a web of data consumable by both human and machines. The resulting web of data and the current web of documents coexist and interconnect via multiple mechanisms, such as the embedded structured data, or the automatic annotation. In this thesis, we introduce a new interactive artifact for the SERP: the “Semantic Snippet”. Semantic Snippets rely on the coexistence of the two webs to facilitate the transfer of knowledge to the user thanks to a semantic contextualization of the user’s information need. It makes apparent the relationships between the information need and the most relevant entities present in the web page. The generation of semantic snippets is mainly based on the automatic annotation of the LOD1’s entities in web pages. The annotated entities have different level of impor- tance, usefulness and relevance. Even with state of the art solutions for the automatic annotations of LOD entities within web pages, there is still a lot of noise in the form of erroneous or off-topic annotations. Therefore, we propose a query-biased algorithm (LDRANK) for the ranking of these entities. LDRANK adopts a strategy based on the linear consensual combination of several sources of prior knowledge (any form of con- textual knowledge, like the textual descriptions for the nodes of the graph) to modify a PageRank-like algorithm. For generating semantic snippets, we use LDRANK to find the more relevant entities in the web page. Then, we use a supervised learning algorithm to link each selected entity to excerpts from the web page that highlight the relationship between the entity and the original information need. In order to evaluate our semantic snippets, we integrate them in ENsEN (Enhanced Search Engine), a software system that enhances the SERP with semantic snippets. Finally, we use crowdsourcing to evaluate the usefulness and the efficiency of ENsEN. N2 - In unserer heutigen Wissensgesellschaft spielen der Erwerb und die Weitergabe von Wissen eine zentrale Rolle. Internetsuchmaschinen fungieren als Werkzeuge für den Erwerb und die Weitergabe von Wissen aus dem Web an den Nutzer. Die Ergebnisliste einer Suchmaschine (SERP) besteht grundsätzlich aus einer Liste von Links und Textauszügen (Snippets). Diese Snippets sollen auf möglichst effiziente Weise ausdrücken inwiefern eine Webseite für die Suchanfrage relevant ist. Als Erweiterung des bestehenden Internets, überführt das semantische Web - auch genannt “Web 3.0” - das momentan vorhandene Internet der unstrukturierten Dokumente in ein Internet der Daten, das sowohl von Menschen als auch Maschinen verwendet werden kann. Das neu geschaffene Internet der Daten und das derzeitige Internet der Dokumente existieren gleichzeitig und sie sind über eine Vielzahl von Mechanismen miteinander verbunden, wie beispielsweise über eingebettete strukturierte Daten oder eine automatische Annotation. In dieser Arbeit stellen wir ein neues interaktives Artefakt für das SERP vor: Das “Semantische Snippet”. Semantische Snippets stützen sich auf die Koexistenz der beiden Arten des Internets um mit Hilfe der Kontextualisierung des Informationsbedürfnisses eines Nutzers die Weitergabe von Wissen zu erleichtern. Sie stellen die Verbindung zwischen dem Informationsbedürfnis und den besonders relevanten Entitäten einer Webseite heraus. Die Erzeugung semantischer Snippets basiert überwiegend auf der automatisierten Annotation von Webseiten mit Entitäten aus der Linking Open Data Cloud (LOD). Die annotierten Entitäten besitzen unterschiedliche Ebenen hinsichtlich Wichtigkeit, Nützlichkeit und Relevanz. Selbst bei state-of-the-art Lösungen zur automatisierten Annotation von LOD- Entitäten in Webseiten, gibt es stets ein großes Maß an Rauschen in Form von fehlerhaften oder themenfremden Annotationen. Wir stellen deshalb einen anfragegetriebenen Algorithmus (LDRANK) für das Ranking dieser Entitäten vor. LDRANK setzt eine Strategie ein, die auf der linearen Konsensus-Kombination (engl. linear consensual combination) mehrerer a-priori Wissensquellen (jedwede Art von Kontextwissen, wie beispielsweise die textuelle Beschreibung der Knoten des Graphen) basiert um damit den PageRank-Algorithmus zu modifizieren. Zur Generierung semantischer Snippets finden wir zunächst mit Hilfe von LDRANK die relevantesten Entitäten in einer Webseite. Anschließend verwenden wir ein überwachtes Lernverfahren um jede ausgewählte Entität denjenigen Abschnitten der Webseite zuzuordnen, die die Beziehung zwischen der Entität und dem ursprünglichen Informationsbedarf am besten herausstellt. Um unsere semantischen Snippets zu evaluieren, integrieren wir sie in ENsEN (Enhanced Search Engine), ein Softwaresystem das SERP um semantische Snippets erweitert. Zum Abschluss bewerten wir die Nu ̈tzlichkeit und die Effizienz von ENsEN mittels Crowdsourcing. KW - Semantic Snippets KW - Entity Ranking KW - Web of Data KW - World Wide Web 3.0 KW - Suchmaschine KW - Suchmaschinenoptimierung KW - Ranking Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3959 ER - TY - THES A1 - Stadler, Thomas T1 - Eine Anwendung der Invariantentheorie auf das Korrespondenzproblem lokaler Bildmerkmale N2 - Als sich in der ersten Hälfte des 19. Jahrhunderts zunehmend mehr bedeutende Mathematiker mit der Suche nach Invarianten beschäftigten, konnte natürlich noch niemand vorhersehen, dass die Invariantentheorie mit Beginn des Computerzeitalters in der Bildverarbeitung bzw. dem Rechnersehen ein äußerst fruchtbares Anwendungsgebiet finden wird. In dieser Arbeit wird eine neue Anwendungsmöglichkeit der Invariantentheorie in der Bildverarbeitung vorgestellt. Dazu werden lokale Bildmerkmale betrachtet. Dabei handelt es sich um die Koordinaten einer Polynomfunktion bzgl. einer geeigneten Orthonormalbasis von P_n(R^2,R), die die zeitintegrierte Sensorinputfunktion auf lokalen Pixelfenstern bestmöglich approximiert. Diese Bildmerkmale werden in vielen Anwendungen eingesetzt, um Objekte in Bildern zu erkennen und zu lokalisieren. Beispiele hierfür sind die Detektion von Werkstücken an einem Fließband oder die Verfolgung von Fahrbahnmarkierungen in Fahrerassistenzsystemen. Modellieren lässt sich die Suche nach einem Muster in einem Suchbild als Paar von Stereobildern, auf denen lokal die affin-lineare Gruppe AGL(R) operiert. Will man also feststellen, ob zwei lokale Pixelfenster in etwa Bilder eines bestimmten dreidimensionalen Oberflächenausschnitts sind, ist zu klären, ob die Bildausschnitte durch eine Operation der Gruppe AGL(R) näherungsweise ineinander übergeführt werden können. Je nach Anwendung genügt es bereits, passende Untergruppen G von AGL(R) zu betrachten. Dank der lokalen Approximation durch Polynomfunktionen induziert die Operation einer Untergruppe G eine Operation auf dem reellen Vektorraum P_n(R^2,R). Damit lässt sich das Korrespondenzproblem auf die Frage reduzieren, ob es eine Transformation T in G gibt so, dass p ungefähr mit der Komposition von q und T für die zugehörigen Approximationspolynome p,q in P_n(R^2,R) gilt. Mit anderen Worten, es ist zu klären, ob sich p und q näherungsweise in einer G-Bahn befinden, eine typische Fragestellung der Invariantentheorie. Da nur lokale Bildausschnitte betrachtet werden, genügt es weiter, Untergruppen G von GL_2(R) zu betrachten. Dann erhält man sofort auch die Antwort für das semidirekte Produkt von R^2 mit G. Besonders interessant für Anwendungen ist hierbei die spezielle orthogonale Gruppe G=SO_2(R) und damit insgesamt die eigentliche Euklidische Gruppe. Für diese Gruppe und spezielle Pixelfenster ist das Korrespondenzproblem bereits gelöst. In dieser Arbeit wird das Problem in eben dieser Konstellation ebenfalls gelöst, allerdings auf elegante Weise mit Methoden der Invariantentheorie. Der Ansatz, der hier vorgestellt wird, ist aber nicht auf diese Gruppe und spezielle Pixelfenster begrenzt, sondern leicht auf weitere Fälle erweiterbar. Dazu ist insbesondere zu klären, wie sich sogenannte fundamentale Invarianten von lokalen Bildmerkmalen, also letztendlich Invarianten von Polynomfunktionen, berechnen lassen, d.h. Erzeugendensysteme der entsprechenden Invariantenringe. Mit deren Hilfe lässt sich die Zugehörigkeit einer Polynomfunktion zur Bahn einer anderen Funktion auf einfache Weise untersuchen. Neben der Vorstellung des Verfahrens zur Korrespondenzfindung und der dafür notwendigen Theorie werden in dieser Arbeit Erzeugendensysteme von Invariantenringen untersucht, die besonders "schöne" Eigenschaften besitzen. Diese schönen Erzeugendensysteme von Unteralgebren werden, analog zu Gröbner-Basen als Erzeugendensysteme von Idealen, SAGBI-Basen genannt ("Subalgebra Analogs to Gröbner Bases for Ideals"). SAGBI-Basen werden hier insbesondere aus algorithmischer Sicht behandelt, d.h. die Berechnung von SAGBI-Basen steht im Vordergrund. Dazu werden verschiedene Algorithmen erarbeitet, deren Korrektheit bewiesen und implementiert. Daraus resultiert ein Software-Paket zu SAGBI-Basen für das Computeralgebrasystem ApCoCoA, dessen Funktionalität in diesem Umfang in keinem Computeralgebrasystem zu finden sein wird. Im Zuge der Umsetzung der einzelnen Algorithmen konnte außerdem die Theorie der SAGBI-Basen an zahlreichen Stellen erweitert werden. KW - Computeralgebra KW - SAGBI-Basen KW - Invariantentheorie KW - Bildverarbeitung KW - (lokale) Bildmerkmale Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4026 ER - TY - THES A1 - Tomashevich, Victor T1 - Fault Tolerance Aspects of Virtual Massive MIMO Systems N2 - Employment of a very large number of antennas is seen as the key technology to provide future users with very high data rates. At the same time, the implementation complexity will rise due to large memories required and sophisticated signal processing algorithms employed. Continuous technology downscaling allows implementation of such complex digital designs. At the same time, its inherent variability and vulnerability to physical disturbances violate the assumption of perfectly reliable hardware operation. This work considers Unique Word OFDM which represents the alternative to the standard Cyclic Prefix OFDM providing superior detection quality. The generalization of Unique Word OFDM to a MIMO system is performed which allows interpretation as a virtual massive MIMO system with only few physical antennas. Detection methods for the introduced generalization are discussed and their performance is quantified. Because of the large memory size required, linear detection represents the cost and performance effective solution. The possible memory errors due to radiation effects or voltage scaling are addressed and the nonlinear MMSE detection algorithm is proposed. This algorithm keeps track of the memory errors and is able to significantly mitigate their effect on the quality of the estimated data. Apart of memory issues, reliability of the actual computational hardware which constitutes the receiver is of concern in this work. An own implementation of the MMSE Sorted Givens Rotations is subjected to transient fault injection. The impact of faults in various parts of the implemented circuit on the detection performance is quantified. Most vulnerable components of the implemented circuit in terms of reliability are identified. Security is another major address of this work, since most current implementations include cryptographic devices. Fault-based attacks on such systems are known to be able to extract the secret key in feasible time. The remaining part of this work addresses such fault injection-based malicious attacks. Countermeasures based on a combination of information and hardware redundancy are considered. Recently introduced robust codes target such attacks by providing guaranteed detection capability. The performance of these codes is assessed by application to actual cryptographic and general purpose circuits. The work introduces metrics that help to identify fault locations in the circuit which could escape detection with high probability. These locations are targeted by transistor resizing that renders fault injection unfeasible. KW - MIMO Systems KW - MIMO KW - Fehlertoleranz Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4047 ER - TY - THES A1 - Wölfl, Andreas T1 - Data Management in Certified Avionics Systems N2 - Data management is a cornerstone for any kind of information system - including the aerospace and aviation sector. In contrast to conventional domains, software development in the avionics domain must adhere to a legally binding certification process, called qualification. The success of the process depends on compliance with international standards, such as DO-178: Software Considerations in Airborne Systems and Equipment Certification. From a software developer's perspective, challenges arise in terms of methods and tools. Techniques that have a potential impact on the deterministic and predictable execution of avionics software are prohibited. The objective of this thesis' research is to develop a scalable method to realize data-management for multi-variant avionics software under the restrictions and constraints of the domain. Since avionics software faces very long-term life-cycles (up to 75 years), a particular focus is being placed on maintenance and evolution. Based on the insights gained in a semi-structured interview at Airbus Helicopters, industrial established approaches to implement qualified avionics software are assessed at first and compared with respect to strengths and weaknesses for data-management afterwards. As a result, a novel development approach is proposed, combining model-based techniques and product-line technology to derive the source code of highly specific data-management variants, as well as the majority of assets required for the qualification process, from a declarative system specification. In order to demonstrate the practicability of the approach in industry, a framework is presented that is deployed and applied at Airbus Helicopters to generate qualifiable data-management components for the variants of the NH90 helicopter. The maintainability is shown by means of a domain-specific optimization, in which the model-based and generative approach is used to establish safe memory overlays at compile-time. Key findings reveal a substantially reduced memory footprint (29,1% in case of a real-world scenario), as well as an significantly facilitated implementation process, which would not be accomplishable using conventional methods for software development in the avionics domain. N2 - Datenverwaltung ist der Grundstein für jegliche Art von Informationssystemen – so auch in der Luft- und Raumfahrt. Im Unterschied zu konventionellen Domänen unterliegt die Software für Avionik-Systeme einem gesetzlich vorgeschriebenen Zertifizierungsprozess, genannt Qualifizierung. Der Erfolg dieses Vorgangs hängt primär von der Einhaltung internationaler Sicherheitsnormen ab. Aus der Sicht eines Software-Entwicklers ergeben sich hier Herausforderungen hinsichtlich erlaubter Methoden und Werkzeuge, denn Techniken, die den deterministischen Ablauf eines Programms gefährden können, sind verboten. Das Ziel dieser Arbeit ist es, ein skalierbares Verfahren zu entwickeln, um eine Datenmanagement-Komponente unter Einhaltung der Sicherheitsnormen für Avionik-Systeme in mehreren Varianten nicht nur zu realisieren, sondern auch langfristig warten zu können (bis zu 75 Jahre). Basierend auf den Erkenntnissen, die durch ein semi-strukturiertes Entwickler-Interview bei Airbus Helicopters gewonnen wurden, werden industriell etablierte Methoden zur Implementierung und Qualifizierung von Avionik-Software zunächst analysiert und anschließend hinsichtlich ihrer Stärken und Schwächen für Datenmanagement bewertet. Als Resultat wird ein neuartiger Ansatz vorgestellt, der durch eine Kombination aus modellbasierten Methoden und Produktlinien-Technologie, sowohl den Quellcode einer spezifischen Datenmanagement-Variante, als auch weitere Erzeugnisse, die für die Qualifizierung zu erbringen sind, aus einer deklarativen Systemspezifikation ableitet. Als Beispiel für die Praktikabilität des Verfahrens wird die Architektur einer Werkzeugkette vorgestellt, die bei Airbus eingesetzt wird, um qualifizierbare Datenmanagement-Varianten für die eingebettete Software des NH90 Helikopters zu generieren. Die Wartbarkeit wird durch eine domänenspezifische Optimierung demonstriert, die durch den modellbasierten und generativen Ansatz eine sichere Überlappung von Speicherbereichen zur Compile-Zeit ermöglicht. Zu den Ergebnissen zählen nicht nur verringerter Speicherverbrauch (29,1% in einem realen Szenario), sondern auch eine effiziente Umsetzung, die mit den etablierten Methoden zur Software-Entwicklung in der Avionik-Domäne nicht zu erreichen wäre. KW - Avionik KW - Datenverarbeitung Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5758 ER - TY - THES A1 - Jovanovic, Philipp T1 - Analysis and Design of Symmetric Cryptographic Algorithms N2 - This doctoral thesis is dedicated to the analysis and the design of symmetric cryptographic algorithms. In the first part of the dissertation, we deal with fault-based attacks on cryptographic circuits which belong to the field of active implementation attacks and aim to retrieve secret keys stored on such chips. Our main focus lies on the cryptanalytic aspects of those attacks. In particular, we target block ciphers with a lightweight and (often) non-bijective key schedule where the derived subkeys are (almost) independent from each other. An attacker who is able to reconstruct one of the subkeys is thus not necessarily able to directly retrieve other subkeys or even the secret master key by simply reversing the key schedule. We introduce a framework based on differential fault analysis that allows to attack block ciphers with an arbitrary number of independent subkeys and which rely on a substitution-permutation network. These methods are then applied to the lightweight block ciphers LED and PRINCE and we show in both cases how to recover the secret master key requiring only a small number of fault injections. Moreover, we investigate approaches that utilize algebraic instead of differential techniques for the fault analysis and discuss advantages and drawbacks. At the end of the first part of the dissertation, we explore fault-based attacks on the block cipher Bel-T which also has a lightweight key schedule but is not based on a substitution-permutation network but instead on the so-called Lai-Massey scheme. The framework mentioned above is thus not usable against Bel-T. Nevertheless, we also present techniques for the case of Bel-T that enable full recovery of the secret key in a very efficient way using differential fault analysis. In the second part of the thesis, we focus on authenticated encryption schemes. While regular ciphers only protect privacy of processed data, authenticated encryption schemes also secure its authenticity and integrity. Many of these ciphers are additionally able to protect authenticity and integrity of so-called associated data. This type of data is transmitted unencrypted but nevertheless must be protected from being tampered with during transmission. Authenticated encryption is nowadays the standard technique to protect in-transit data. However, most of the currently deployed schemes have deficits and there are many leverage points for improvements. With NORX we introduce a novel authenticated encryption scheme supporting associated data. This algorithm was designed with high security, efficiency in both hardware and software, simplicity, and robustness against side-channel attacks in mind. Next to its specification, we present special features, security goals, implementation details, extensive performance measurements and discuss advantages over currently deployed standards. Finally, we describe our preliminary security analysis where we investigate differential and rotational properties of NORX. Noteworthy are in particular the newly developed techniques for differential cryptanalysis of NORX which exploit the power of SAT- and SMT-solvers and have the potential to be easily adaptable to other encryption schemes as well. N2 - Diese Doktorarbeit beschäftigt sich mit der Analyse und dem Entwurf von symmetrischen kryptographischen Algorithmen. Im ersten Teil der Dissertation befassen wir uns mit fehlerbasierten Angriffen auf kryptographische Schaltungen, welche dem Gebiet der aktiven Seitenkanalangriffe zugeordnet werden und auf die Rekonstruktion geheimer Schlüssel abzielen, die auf diesen Chips gespeichert sind. Unser Hauptaugenmerk liegt dabei auf den kryptoanalytischen Aspekten dieser Angriffe. Insbesondere beschäftigen wir uns dabei mit Blockchiffren, die leichtgewichtige und eine (oft) nicht-bijektive Schlüsselexpansion besitzen, bei denen die erzeugten Teilschlüssel voneinander (nahezu) unabhängig sind. Ein Angreifer, dem es gelingt einen Teilschlüssel zu rekonstruieren, ist dadurch nicht in der Lage direkt weitere Teilschlüssel oder sogar den Hauptschlüssel abzuleiten indem er einfach die Schlüsselexpansion umkehrt. Wir stellen Techniken basierend auf differenzieller Fehleranalyse vor, die es ermöglichen Blockchiffren zu analysieren, welche eine beliebige Anzahl unabhängiger Teilschlüssel einsetzen und auf Substitutions-Permutations Netzwerken basieren. Diese Methoden werden im Anschluss auf die leichtgewichtigen Blockchiffren LED und PRINCE angewandt und wir zeigen in beiden Fällen wie der komplette geheime Schlüssel mit einigen wenigen Fehlerinjektionen rekonstruiert werden kann. Darüber hinaus untersuchen wir Methoden, die algebraische statt differenzielle Techniken der Fehleranalyse einsetzen und diskutieren deren Vor- und Nachteile. Am Ende des ersten Teils der Dissertation befassen wir uns mit fehlerbasierten Angriffen auf die Blockchiffre Bel-T, welche ebenfalls eine leichtgewichtige Schlüsselexpansion besitzt jedoch nicht auf einem Substitutions-Permutations Netzwerk sondern auf dem sogenannten Lai-Massey Schema basiert. Die oben genannten Techniken können daher bei Bel-T nicht angewandt werden. Nichtsdestotrotz werden wir auch für den Fall von Bel-T Verfahren vorstellen, die in der Lage sind den vollständigen geheimen Schlüssel sehr effizient mit Hilfe von differenzieller Fehleranalyse zu rekonstruieren. Im zweiten Teil der Doktorarbeit beschäftigen wir uns mit authentifizierenden Verschlüsselungsverfahren. Während gewöhnliche Chiffren nur die Vertraulichkeit der verarbeiteten Daten sicherstellen, gewährleisten authentifizierende Verschlüsselungsverfahren auch deren Authentizität und Integrität. Viele dieser Chiffren sind darüber hinaus in der Lage auch die Authentizität und Integrität von sogenannten assoziierten Daten zu gewährleisten. Daten dieses Typs werden in nicht-verschlüsselter Form übertragen, müssen aber dennoch gegen unbefugte Veränderungen auf dem Transportweg geschützt sein. Authentifizierende Verschlüsselungsverfahren bilden heutzutage die Standardtechnologie um Daten während der Übertragung zu beschützen. Aktuell eingesetzte Verfahren weisen jedoch oftmals Defizite auf und es existieren vielfältige Ansatzpunkte für Verbesserungen. Mit NORX stellen wir ein neuartiges authentifizierendes Verschlüsselungsverfahren vor, welches assoziierte Daten unterstützt. Dieser Algorithmus wurde vor allem im Hinblick auf Einsatzgebiete mit hohen Sicherheitsanforderungen, Effizienz in Hardware und Software, Einfachheit, und Robustheit gegenüber Seitenkanalangriffen entwickelt. Neben der Spezifikation präsentieren wir besondere Eigenschaften, angestrebte Sicherheitsziele, Details zur Implementierung, umfassende Performanz-Messungen und diskutieren Vorteile gegenüber aktuellen Standards. Schließlich stellen wir Ergebnisse unserer vorläufigen Sicherheitsanalyse vor, bei der wir uns vor allem auf differenzielle Merkmale und Rotationseigenschaften von NORX konzentrieren. Erwähnenswert sind dabei vor allem die für die differenzielle Kryptoanalyse von NORX entwickelten Techniken, die auf die Effizienz von SAT- und SMT-Solvern zurückgreifen und das Potential besitzen relativ einfach auch auf andere Verschlüsselungsverfahren übertragen werden zu können. KW - cryptography KW - cryptanalysis KW - authenticated encryption KW - NORX KW - fault-based attacks KW - Kryptologie KW - Computersicherheit Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3319 ER - TY - THES A1 - Ruppert, Julia T1 - Asymptotic Expansion for the Time Evolution of the Probability Distribution Given by the Brownian Motion on Semialgebraic Sets N2 - In this thesis, we examine whether the probability distribution given by the Brownian Motion on a semialgebraic set is definable in an o-minimal structure and we establish asymptotic expansions for the time evolution. We study the probability distribution as an example for the occurrence of special parameterized integrals of a globally subanalytic function and the exponential function of a globally subanalytic function. This work is motivated by the work of Comte, Lion and Rolin, which considered parameterized integrals of globally subanalytic functions, of Cluckers and Miller, which examined parameterized integrals of constructible functions, and by the work of Cluckers, Comte, Miller, Rolin and Servi, which treated oscillatory integrals of globally subanalytic functions. In the one dimensional case we show that the probability distribution on a family of sets, which are definable in an o-minimal structure, are definable in the Pfaffian closure. In the two-dimensional case we investigate asymptotic expansions for the time evolution. As time t approaches zero, we show that the integrals behave like a Puiseux series, which is not necessarily convergent. As t tends towards infinity, we show that the probability distribution is definable in the expansion of the real ordered field by all restricted analytic functions if the semialgebraic set is bounded. For this purpose, we apply results for parameterized integrals of globally subanalytic functions of Lion and Rolin. By establishing the asymptotic expansion of the integrals over an unbounded set, we demonstrate that this expansion has the form of convergent Puiseux series with negative exponents and their logarithm. Subsequently, we get that the asymptotic expansion is definable in an o-minimal structure. Finally, we study the three-dimensional case and give the proof that the probability distribution given by the Brownian Motion behaves like a Puiseux series as time t tends towards zero. As t approaches infinity and the semialgebraic set is bounded, it can be ascertained that the probability distribution has the form of a constructible function by results of Cluckers and Miller and therefore it is definable in an o-minimal structure. If the semialgebraic set is unbounded, we establish the asymptotic expansions and prove that the probability distribution given by the Brownian Motion on unbounded sets has an asymptotic expansion of the form of a constructible function. In consequence of that, the asymptotic expansion is definable in an o-minimal structure. KW - o-minimality KW - asymptotic expansions KW - globally subanalytic sets KW - exponential parameterized integrals KW - Brownian Motion KW - Brownsche Bewegung KW - O-Minimalität KW - Asymptotische Entwicklung Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5069 ER - TY - THES A1 - Reislhuber, Josef T1 - Optical Graph Recognition N2 - Graphs are an important model for the representation of structural information between objects. One identifies objects and nodes as well as a binary relation between objects and edges. Graphs have many uses, e. g., in social sciences, life sciences and engineering. There are two primary representations: abstract and visual. The abstract representation is well suited for processing graphs by computers and is given by an adjacency list, an adjacency matrix or any abstract data structure. A visual representation is used by human users who prefer a picture. Common terms are diagram, scheme, plan, or network. The objective of Graph Drawing is to transform a graph into a visual representation called the drawing of a graph. The goal is a “nice” drawing. In this thesis we introduce Optical Graph Recognition. Optical Graph Recognition (OGR) reverses Graph Drawing and transforms a digital image of a graph into an abstract representation. Our approach consists of four phases: Preprocessing where we determine which pixels of an image are part of the graph, Segmentation where we recognize the nodes, Topology Recognition where we detect the edges and Postprocessing where we enrich the recognized graph with additional information. We apply established digital image processing methods and make use of the special property that the image contains nodes that are connected by edges. We have focused on developing algorithms that need as little parameters as possible or to automatically calibrate the parameters. Most false recognition results are caused by crossing edges as this makes tracing the edges difficult and can lead to other recognition errors. We have evaluated hand-drawn and computer-drawn graphs. Our algorithms have a very high recognition rate for computer-drawn graphs, e. g., from a set of 100000 computer-drawn graphs over 90% were correctly recognized. Most false recognition results where observed for hand-drawn graphs as they can include drawing errors and inaccuracies. For universal usability we have implemented a prototype called OGRup for mobile devices like smartphones or tablet computers. With our software it is possible to directly take a picture of a graph via a built in camera, recognize the graph, and then use the result for further processing. Furthermore, in order to gain more insight into the way a person draws a graph by hand, we have conducted a field study. KW - Bildverarbeitung KW - Graphenzeichnen Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5159 ER - TY - THES A1 - de Ponte Müller, Fabian T1 - Cooperative Relative Positioning for Vehicular Environments N2 - Fahrerassistenzsysteme sind ein wesentlicher Baustein zur Steigerung der Sicherheit im Straßenverkehr. Vor allem sicherheitsrelevante Applikationen benötigen eine genaue Information über den Ort und der Geschwindigkeit der Fahrzeuge in der unmittelbaren Umgebung, um mögliche Gefahrensituationen vorherzusehen, den Fahrer zu warnen oder eigenständig einzugreifen. Repräsentative Beispiele für Assistenzsysteme, die auf eine genaue, kontinuierliche und zuverlässige Relativpositionierung anderer Verkehrsteilnehmer angewiesen sind, sind Notbremsassitenten, Spurwechselassitenten und Abstandsregeltempomate. Moderne Lösungsansätze benutzen Umfeldsensorik wie zum Beispiel Radar, Laser Scanner oder Kameras, um die Position benachbarter Fahrzeuge zu schätzen. Dieser Sensorsysteme gemeinsame Nachteile sind deren limitierte Erfassungsreichweite und die Notwendigkeit einer direkten und nicht blockierten Sichtlinie zum Nachbarfahrzeug. Kooperative Lösungen basierend auf einer Fahrzeug-zu-Fahrzeug Kommunikation können die eigene Wahrnehmungsreichweite erhöhen, in dem Positionsinformationen zwischen den Verkehrsteilnehmern ausgetauscht werden. In dieser Dissertation soll die Möglichkeit der kooperativen Relativpositionierung von Straßenfahrzeugen mittels Fahrzeug-zu-Fahrzeug Kommunikation auf ihre Genauigkeit, Kontinuität und Robustheit untersucht werden. Anstatt die in jedem Fahrzeug unabhängig ermittelte Position zu übertragen, werden in einem neuartigem Ansatz GNSS-Rohdaten, wie Pseudoranges und Doppler-Messungen, ausgetauscht. Dies hat den Vorteil, dass sich korrelierte Fehler in beiden Fahrzeugen potentiell herauskürzen. Dies wird in dieser Dissertation mathematisch untersucht, simulativ modelliert und experimentell verifiziert. Um die Zuverlässigkeit und Kontinuität auch in "gestörten" Umgebungen zu erhöhen, werden in einem Bayesischen Filter die GNSS-Rohdaten mit Inertialsensormessungen aus zwei Fahrzeugen fusioniert. Die Validierung des Sensorfusionsansatzes wurde im Rahmen dieser Dissertation in einem Verkehrs- sowie in einem GNSS-Simulator durchgeführt. Zur experimentellen Untersuchung wurden zwei Testfahrzeuge mit den verschiedenen Sensoren ausgestattet und Messungen in diversen Umgebungen gefahren. In dieser Arbeit wird gezeigt, dass auf Autobahnen, die Relativposition eines anderen Fahrzeugs mit einer Genauigkeit von unter einem Meter kontinuierlich geschätzt werden kann. Eine hohe Zuverlässigkeit in der longitudinalen und lateralen Richtung können erzielt werden und das System erweist 90% der Zeit eine Unsicherheit unter 2.5m. In ländlichen Umgebungen wächst die Unsicherheit in der relativen Position. Mit Hilfe der on-board Sensoren können Fehler bei der Fahrt durch Wälder und Dörfer korrekt gestützt werden. In städtischen Umgebungen werden die Limitierungen des Systems deutlich. Durch die erschwerte Schätzung der Fahrtrichtung des Ego-Fahrzeugs ist vor Allem die longitudinale Komponente der Relativen Position in städtischen Umgebungen stark verfälscht. N2 - Advanced driver assistance systems play an important role in increasing the safety on today's roads. The knowledge about the other vehicles' positions is a fundamental prerequisite for numerous safety critical applications, making it possible to foresee critical situations, warn the driver or autonomously intervene. Forward collision avoidance systems, lane change assistants or adaptive cruise control are examples of safety relevant applications that require an accurate, continuous and reliable relative position of surrounding vehicles. Currently, the positions of surrounding vehicles is estimated by measuring the distance with e.g. radar, laser scanners or camera systems. However, all these techniques have limitations in their perception range, as all of them can only detect objects in their line-of-sight. The limited perception range of today's vehicles can be extended in future by using cooperative approaches based on Vehicle-to-Vehicle (V2V) communication. In this thesis, the capabilities of cooperative relative positioning for vehicles will be assessed in terms of its accuracy, continuity and reliability. A novel approach where Global Navigation Satellite System (GNSS) raw data is exchanged between the vehicles is presented. Vehicles use GNSS pseudorange and Doppler measurements from surrounding vehicles to estimate the relative positioning vector in a cooperative way. In this thesis, this approach is shown to outperform the absolute position subtraction as it is able to effectively cancel out common errors to both GNSS receivers. This is modeled theoretically and demonstrated empirically using simulated signals from a GNSS constellation simulator. In order to cope with GNSS outages and to have a sufficiently good relative position estimate even in strong multipath environments, a sensor fusion approach is proposed. In addition to the GNSS raw data, inertial measurements from speedometers, accelerometers and turn rate sensors from each vehicle are exchanged over V2V communication links. A Bayesian approach is applied to consider the uncertainties inherently to each of the information sources. In a dynamic Bayesian network, the temporal relationship of the relative position estimate is predicted by using relative vehicle movement models. Also real world measurements in highway, rural and urban scenarios are performed in the scope of this work to demonstrate the performance of the cooperative relative positioning approach based on sensor fusion. The results show that the relative position of another vehicle towards the ego vehicle can be estimated with sub-meter accuracy in highway scenarios. Here, good reliability and 90% availability with an uncertainty of less than 2.5m is achieved. In rural environments, drives through forests and towns are correctly bridged with the support of on-board sensors. In an urban environment, the difficult estimation of the ego vehicle heading has a mayor impact in the relative position estimate, yielding large errors in its longitudinal component. KW - Fahrerassistenzsystem Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5411 ER - TY - THES A1 - Hanauer, Kathrin T1 - Linear Orderings of Sparse Graphs N2 - The Linear Ordering problem consists in finding a total ordering of the vertices of a directed graph such that the number of backward arcs, i.e., arcs whose heads precede their tails in the ordering, is minimized. A minimum set of backward arcs corresponds to an optimal solution to the equivalent Feedback Arc Set problem and forms a minimum Cycle Cover. Linear Ordering and Feedback Arc Set are classic NP-hard optimization problems and have a wide range of applications. Whereas both problems have been studied intensively on dense graphs and tournaments, not much is known about their structure and properties on sparser graphs. There are also only few approximative algorithms that give performance guarantees especially for graphs with bounded vertex degree. This thesis fills this gap in multiple respects: We establish necessary conditions for a linear ordering (and thereby also for a feedback arc set) to be optimal, which provide new and fine-grained insights into the combinatorial structure of the problem. From these, we derive a framework for polynomial-time algorithms that construct linear orderings which adhere to one or more of these conditions. The analysis of the linear orderings produced by these algorithms is especially tailored to graphs with bounded vertex degrees of three and four and improves on previously known upper bounds. Furthermore, the set of necessary conditions is used to implement exact and fast algorithms for the Linear Ordering problem on sparse graphs. In an experimental evaluation, we finally show that the property-enforcing algorithms produce linear orderings that are very close to the optimum and that the exact representative delivers solutions in a timely manner also in practice. As an additional benefit, our results can be applied to the Acyclic Subgraph problem, which is the complementary problem to Feedback Arc Set, and provide insights into the dual problem of Feedback Arc Set, the Arc-Disjoint Cycles problem. KW - directed graph KW - graph algorithms KW - feedback arc set KW - linear ordering KW - cycle cover KW - Graphentheorie KW - Lineares Ordnungsproblem KW - Schwach besetzte Matrix Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5524 ER - TY - THES A1 - Kell, Christian T1 - A Structure-based Attack on the Linearized Braid Group-based Diffie-Hellman Conjugacy Problem in Combination with an Attack using Polynomial Interpolation and the Chinese Remainder Theorem N2 - This doctoral thesis is dedicated to improve a linear algebra attack on the so-called braid group-based Diffie-Hellman conjugacy problem (BDHCP). The general procedure of the attack is to transform a BDHCP to the problem of solving several simultaneous matrix equations. A first improvement is achieved by reducing the solution space of the matrix equations to matrices that have a specific structure, which we call here the left braid structure. Using the left braid structure the number of matrix equations to be solved reduces to one. Based on the left braid structure we are further able to formulate a structure-based attack on the BDHCP. That is to transform the matrix equation to a system of linear equations and exploiting the structure of the corresponding extended coefficient matrix, which is induced by the left braid structure of the solution space. The structure-based attack then has an empirically high probability to solve the BDHCP with significantly less arithmetic operations than the original attack. A third improvement of the original linear algebra attack is to use an algorithm that combines Gaussian elimination with integer polynomial interpolation and the Chinese remainder theorem (CRT), instead of fast matrix multiplication as suggested by others. The major idea here is to distribute the task of solving a system of linear equations over a giant finite field to several much smaller finite fields. Based on our empirically measured bounds for the degree of the polynomials to be interpolated and the bit size of the coefficients and integers to be recovered via the CRT, we conclude an improvement of the run time complexity of the original algorithm by a factor of n^8 bit operations in the best case, and still n^6 in the worst case. KW - Linear algebra attack KW - Braid group-based cryptography KW - Row echelon form calculation using polynomial interpolation and the chinese remainder theorem KW - Diffie-Hellman conjugacy problem KW - Kryptologie KW - Zopfgruppe KW - Diffie-Hellman-Algorithmus Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-6476 ER - TY - THES A1 - Lehner, Sabrina T1 - The Asymptotic Behaviour of the Riemann Mapping Function at Analytic Cusps N2 - The well-known Riemann Mapping Theorem states the existence of a conformal map of a simply connected proper domain of the complex plane onto the upper half plane. One of the main topics in geometric function theory is to investigate the behaviour of the mapping functions at the boundary of such domains. In this work, we always assume that a piecewise analytic boundary is given. Hereby, we have to distinguish regular and singular boundary points. While the asymptotic behaviour for regular boundary points can be investigated by using the Schwarz Reflection at analytic arcs, the situation for singular boundary points is far more complicated. In the latter scenario two cases have to be differentiated: analytic corners and analytic cusps. The first part of the thesis deals with the asymptotic behaviour at analytic corners where the opening angle is greater than 0. The results of Lichtenstein and Warschawski on the asymptotic behaviour of the Riemann map and its derivatives at an analytic corner are presented as well as the much stronger result of Lehman that the mapping function can be developed in a certain generalised power series which in turn enables to examine the o-minimal content of the Riemann Mapping Theorem. To obtain a similar statement for domains with analytic cusps, it is necessary to investigate the asymptotic behaviour of a Riemann map at the cusp and based on this result to determine the asymptotic power series expansion. Therefore, the aim of the second part of this work is to investigate the asymptotic behaviour of a Riemann map at an analytic cusp. A simply connected domain has an analytic cusp if the boundary is locally given by two analytic arcs such that the interior angle vanishes. Besides the asymptotic behaviour of the mapping function, the behaviour of its derivatives, its inverse, and the derivatives of the inverse are analysed. Finally, we present a conjecture on the asymptotic power series expansion of the mapping function at an analytic cusp. N2 - Der wohlbekannte Riemannsche Abbildungssatz liefert die Existenz einer konformen Abbildung eines einfach zusammenhängenden, echten Teilgebietes der komplexen Ebene auf die obere Halbebene. Die Untersuchung des Verhaltens solcher Abbildungen am Rand der Gebiete ist ein zentrales Thema der geometrischen Funktionentheorie. In der vorliegenden Arbeit gehen wir stets von einem stückweise analytischen Rand aus. Dabei müssen wir reguläre und singuläre Randpunkte unterscheiden. Während das Verhalten einer Riemann-Abbildung an regulären Randpunkten mit Hilfe des Schwarzschen Spiegelungsprinzips an analytischen Kurvenbögen einfach zu bestimmen ist, gestaltet sich dies in der Situation von singulären Randpunkten sehr viel komplizierter. In diesem Fall müssen wir erneut eine Unterscheidung treffen, nämlich ob es sich um eine analytische Ecke oder eine analytische Spitze handelt. Der erste Teil der Dissertation beschäftigt sich mit dem asymptotischen Verhalten einer Riemann-Abbildung an analytischen Ecken. Eine solche liegt vor, falls der Öffnungswinkel zwischen den analytischen Kurvenstücken an dem singulären Randpunkt größer als 0 ist. Es werden die Ergebnisse von Lichtenstein und Warschawski präsentiert, die sich mit dem Verhalten der Riemann-Abbildung und deren Ableitungen beschäftigt haben, sowie das stärkere Ergebnis von Lehman welches besagt, dass die Abbildung in eine verallgemeinerte Potenzreihe entwickelt werden kann. Unter Verwendung dieses Resultats konnte bereits der o-minimale Gehalt des Riemannschen Abbildungssatzes untersucht werden. Um ein ähnliches Ergebnis für den Fall, dass das Gebiet analytische Spitzen hat, zu erhalten, benötigen wir zunächst das asymptotische Verhalten der Riemann-Abbildung an einer Spitze. Darauf aufbauend kann die asymptotische Reihenentwicklung untersucht werden. Daher zielt der zweite Abschnitt dieser Arbeit darauf ab, das Verhalten der Abbildung an einer Spitze zu bestimmen. Dabei sprechen wir von einer analytischen Spitze, wenn der Rand des Gebietes lokal durch zwei reguläre analytische Bögen gegeben ist, deren Öffnungswinkel verschwindet. Neben dem asymptotischen Verhalten der Abbildung wird auch das Verhalten der Ableitungen, ihrer Umkehrfunktion und deren Ableitungen untersucht. Abschließend präsentieren wir eine Vermutung über die asymptotische Reihenentwicklung der Abbildung an einer analytischen Spitze. KW - Riemann mapping theorem KW - analytic cusp KW - asymptotic behaviour KW - boundary behaviour KW - Geometrische Funktionentheorie KW - Randverhalten KW - Riemannscher Abbildungssatz Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3587 ER - TY - THES A1 - Petit, Albin T1 - Introducing Privacy in Current Web Search Engines N2 - During the last few years, the technological progress in collecting, storing and processing a large quantity of data for a reasonable cost has raised serious privacy issues. Privacy concerns many areas, but is especially important in frequently used services like search engines (e.g., Google, Bing, Yahoo!). These services allow users to retrieve relevant content on the Internet by exploiting their personal data. In this context, developing solutions to enable users to use these services in a privacy-preserving way is becoming increasingly important. In this thesis, we introduce SimAttack an attack against existing protection mechanism to query search engines in a privacy-preserving way. This attack aims at retrieving the original user query. We show with this attack that three representative state-of-the-art solutions do not protect the user privacy in a satisfactory manner. We therefore develop PEAS a new protection mechanism that better protects the user privacy. This solution leverages two types of protection: hiding the user identity (with a succession of two nodes) and masking users' queries (by combining them with several fake queries). To generate realistic fake queries, PEAS exploits previous queries sent by the users in the system. Finally, we present mechanisms to identify sensitive queries. Our goal is to adapt existing protection mechanisms to protect sensitive queries only, and thus save user resources (e.g., CPU, RAM). We design two modules to identify sensitive queries. By deploying these modules on real protection mechanisms, we establish empirically that they dramatically improve the performance of the protection mechanisms. KW - Privacy KW - Search Engine KW - Unlinkability KW - Indistinguishability KW - Suchmaschine KW - Datensicherung KW - Computersicherheit KW - Privatsphäre Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4652 ER - TY - THES A1 - Kriegl, Markus T1 - Generalizations and Applications of Border Bases N2 - This doctoral thesis is devoted to generalize border bases to the module setting and to apply them in various ways. First, we generalize the theory of border bases to finitely generated modules over a polynomial ring. We characterize these generalized border bases and show that we can compute them. As an application, we are able to characterize subideal border bases in various new ways and give a new algorithm for their computation. Moreover, we prove Schreyer's Theorem for border bases of submodules of free modules of finite rank over a polynomial ring. In the second part of this thesis, we study the effect of homogenization to border bases of zero-dimensional ideals. This yields the new concept of projective border bases of homogeneous one-dimensional ideals. We show that there is a one-to-one correspondence between projective border bases and zero-dimensional closed subschemes of weighted projective spaces that have no point on the hyperplane at infinity. Applying that correspondence, we can characterize uniform zero-dimensional closed subschemes of weighted projective spaces that have a rational support over the base field in various ways. Finally, we introduce projective border basis schemes as specific subschemes of border basis schemes. We show that these projective border basis schemes parametrize all zero-dimensional closed subschemes of a weighted projective space whose defining ideals possess a projective border basis. Assuming that the base field is algebraically closed, we are able to prove that the set of all closed points of a projective border basis scheme that correspond to a uniform subscheme is a constructive set with respect to the Zariski topology. KW - (generalized) border bases KW - Schreyer's theorem KW - weighted projective spaces KW - zero-dimensional projective schemes KW - uniformity conditions Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3628 ER - TY - THES A1 - Liebig, Jörg T1 - Analysis and Transformation of Configurable Systems N2 - Static analysis tools and transformation engines for source code belong to the standard equipment of a software developer. Their use simplifies a developer's everyday work of maintaining and evolving software systems significantly and, hence, accounts for much of a developer's programming efficiency and programming productivity. This is also beneficial from a financial point of view, as programming errors are early detected and avoided in the the development process, thus the use of static analysis tools reduces the overall software-development costs considerably. In practice, software systems are often developed as configurable systems to account for different requirements of application scenarios and use cases. To implement configurable systems, developers often use compile-time implementation techniques, such as preprocessors, by using #ifdef directives. Configuration options control the inclusion and exclusion of #ifdef-annotated source code and their selection/deselection serve as an input for generating tailor-made system variants on demand. Existing configurable systems, such as the linux kernel, often provide thousands of configuration options, forming a huge configuration space with billions of system variants. Unfortunately, existing tool support cannot handle the myriads of system variants that can typically be derived from a configurable system. Analysis and transformation tools are not prepared for variability in source code, and, hence, they may process it incorrectly with the result of an incomplete and often broken tool support. We challenge the way configurable systems are analyzed and transformed by introducing variability-aware static analysis tools and a variability-aware transformation engine for configurable systems' development. The main idea of such tool support is to exploit commonalities between system variants, reducing the effort of analyzing and transforming a configurable system. In particular, we develop novel analysis approaches for analyzing the myriads of system variants and compare them to state-of-the-art analysis approaches (namely sampling). The comparison shows that variability-aware analysis is complete (with respect to covering the whole configuration space), efficient (it outperforms some of the sampling heuristics), and scales even to large software systems. We demonstrate that variability-aware analysis is even practical when using it with non-trivial case studies, such as the linux kernel. On top of variability-aware analysis, we develop a transformation engine for C, which respects variability induced by the preprocessor. The engine provides three common refactorings (rename identifier, extract function, and inline function) and overcomes shortcomings (completeness, use of heuristics, and scalability issues) of existing engines, while still being semantics-preserving with respect to all variants and being fast, providing an instantaneous user experience. To validate semantics preservation, we extend a standard testing approach for refactoring engines with variability and show in real-world case studies the effectiveness and scalability of our engine. In the end, our analysis and transformation techniques show that configurable systems can efficiently be analyzed and transformed (even for large-scale systems), providing the same guarantees for configurable systems as for standard systems in terms of detecting and avoiding programming errors. KW - Configurable Systems KW - Variability-aware Analysis KW - Variability-aware Refactoring KW - Software Product Lines KW - Refactoring KW - Statische Analyse KW - Präprozessor KW - Softwarewartung KW - C Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-2996 ER - TY - THES A1 - Braun, Bastian T1 - Web-based Secure Application Control N2 - The world wide web today serves as a distributed application platform. Its origins, however, go back to a simple delivery network for static hypertexts. The legacy from these days can still be observed in the communication protocol used by increasingly sophisticated clients and applications. This thesis identifies the actual security requirements of modern web applications and shows that HTTP does not fit them: user and application authentication, message integrity and confidentiality, control-flow integrity, and application-to-application authorization. We explore the other protocols in the web stack and work out why they can not fill the gap. Our analysis shows that the underlying problem is the connectionless property of HTTP. However, history shows that a fresh start with web communication is far from realistic. As a consequence, we come up with approaches that contribute to meet the identified requirements. We first present impersonation attack vectors that begin before the actual user authentication, i.e. when secure web interaction and authentication seem to be unnecessary. Session fixation attacks exploit a responsibility mismatch between the web developer and the used web application framework. We describe and compare three countermeasures on different implementation levels: on the source code level, on the framework level, and on the network level as a reverse proxy. Then, we explain how the authentication credentials that are transmitted for the user login, i.e. the password, and for session tracking, i.e. the session cookie, can be complemented by browser-stored and user-based secrets respectively. This way, an attacker can not hijack user accounts only by phishing the user's password because an additional browser-based secret is required for login. Also, the class of well-known session hijacking attacks is mitigated because a secret only known by the user must be provided in order to perform critical actions. In the next step, we explore alternative approaches to static authentication credentials. Our approach implements a trusted UI and a mutually authenticated session using signatures as a means to authenticate requests. This way, it establishes a trusted path between the user and the web application without exchanging reusable authentication credentials. As a downside, this approach requires support on the client side and on the server side in order to provide maximum protection. Another approach avoids client-side support but can not implement a trusted UI and is thus susceptible to phishing and clickjacking attacks. Our approaches described so far increase the security level of all web communication at all time. This is why we investigate adaptive security policies that fit the actual risk instead of permanently restricting all kinds of communication including non-critical requests. We develop a smart browser extension that detects when the user is authenticated on a website meaning that she can be impersonated because all requests carry her identity proof. Uncritical communication, however, is released from restrictions to enable all intended web features. Finally, we focus on attacks targeting a web application's control-flow integrity. We explain them thoroughly, check whether current web application frameworks provide means for protection, and implement two approaches to protect web applications: The first approach is an extension for a web application framework and provides protection based on its configuration by checking all requests for policy conformity. The second approach generates its own policies ad hoc based on the observed web traffic and assuming that regular users only click on links and buttons and fill forms but do not craft requests to protected resources. N2 - Das heutige World Wide Web ist eine verteilte Plattform für Anwendungen aller Art: von einfachen Webseiten über Online Banking, E-Mail, multimediale Unterhaltung bis hin zu intelligenten vernetzten Häusern und Städten. Seine Ursprünge liegen allerdings in einem einfachen Netzwerk zur Übermittlung statischer Inhalte auf der Basis von Hypertexten. Diese Ursprünge lassen sich noch immer im verwendeten Kommunikationsprotokoll HTTP identifizieren. In dieser Arbeit untersuchen wir die Sicherheitsanforderungen moderner Web-Anwendungen und zeigen, dass HTTP diese Anforderungen nicht erfüllen kann. Zu diesen Anforderungen gehören die Authentifikation von Benutzern und Anwendungen, die Integrität und Vertraulichkeit von Nachrichten, Kontrollflussintegrität und die gegenseitige Autorisierung von Anwendungen. Wir untersuchen die Web-Protokolle auf den unteren Netzwerk-Schichten und zeigen, dass auch sie nicht die Sicherheitsanforderungen erfüllen können. Unsere Analyse zeigt, dass das grundlegende Problem in der Verbindungslosigkeit von HTTP zu finden ist. Allerdings hat die Geschichte gezeigt, dass ein Neustart mit einem verbesserten Protokoll keine Option für ein gewachsenes System wie das World Wide Web ist. Aus diesem Grund beschäftigt sich diese Arbeit mit unseren Beiträgen zu sicherer Web-Kommunikation auf der Basis des existierenden verbindungslosen HTTP. Wir beginnen mit der Beschreibung von Session Fixation-Angriffen, die bereits vor der eigentlichen Anmeldung des Benutzers an der Web-Anwendung beginnen und im Erfolgsfall die temporäre Übernahme des Benutzerkontos erlauben. Wir präsentieren drei Gegenmaßnahmen, die je nach Eingriffsmöglichkeiten in die Web-Anwendung umgesetzt werden können. Als nächstes gehen wir auf das Problem ein, dass Zugangsdaten im WWW sowohl zwischen den Teilnehmern zu Authentifikationszwecken kommuniziert werden als auch für jeden, der Kenntnis dieser Daten erlangt, wiederverwendbar sind. Unsere Ansätze binden das Benutzerpasswort an ein im Browser gespeichertes Authentifikationsmerkmal und das sog. Session-Cookie an ein Geheimnis, das nur dem Benutzer und der Web-Anwendung bekannt ist. Auf diese Weise kann ein Angreifer weder ein gestohlenes Passwort noch ein Session-Cookie allein zum Zugriff auf das Benutzerkonto verwenden. Darauffolgend beschreiben wir ein Authentifikationsprotokoll, das vollständig auf die Übermittlung geheimer Zugangsdaten verzichtet. Unser Ansatz implementiert eine vertrauenswürdige Benutzeroberfläche und wirkt so gegen die Manipulation derselben in herkömmlichen Browsern. Während die bisherigen Ansätze die Sicherheit jeglicher Web-Kommunikation erhöhen, widmen wir uns der Frage, inwiefern ein intelligenter Browser den Benutzer - wenn nötig - vor Angriffen bewahren kann und - wenn möglich - eine ungehinderte Kommunikation ermöglichen kann. Damit trägt unser Ansatz zur Akzeptanz von Sicherheitslösungen bei, die ansonsten regelmäßig als lästige Einschränkungen empfunden werden. Schließlich legen wir den Fokus auf die Kontrollflussintegrität von Web-Anwendungen. Bösartige Benutzer können den Zustand von Anwendungen durch speziell präparierte Folgen von Anfragen in ihrem Sinne manipulieren. Unsere Ansätze filtern Benutzeranfragen, die von der Anwendung nicht erwartet wurden, und lassen nur solche Anfragen passieren, die von der Anwendung ordnungsgemäß verarbeitet werden können. KW - Computersicherheit KW - Datensicherung KW - Internet Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3048 ER - TY - THES A1 - Sipal, Bilge T1 - Border Basis Schemes N2 - The basic idea of border basis theory is to describe a zero-dimensional ring P/I by an order ideal of terms whose residue classes form a K-vector space basis of P/I. The O-border basis scheme is a scheme that parametrizes all zero-dimensional ideals that have an O-border basis. In general, the O-border basis scheme is not an affine space. Subsequently, in [Huib09] it is proved that if an order ideal with "d" elements is defined in a two-dimensional polynomial ring and it is of some special shapes, then the O-border basis scheme is isomorphic to the affine space of dimension 2d. This thesis is dedicated to find a more general condition for an O-border basis scheme to be isomorphic to an affine space of dimension "nd" that is independent of the shape of the order ideal with "d" elements and "n" is the dimension of the polynomial ring that the order ideal is defined in. We accomplish this in 6 Chapters. In Chapters 2 and 3 we develop the concepts and properties of border basis schemes. In Chapter 4 we transfer the smoothness criterion (see [Huib05]) for the point (0,...,0) in a Hilbert scheme of points to the monomial point of the border basis scheme by employing the tools from border basis theory. In Chapter 5 we explain trace and Jacobi identity syzygies of the defining equations of a O-border basis scheme and characterize them by the arrow grading. In Chapter 6 we give a criterion for the isomorphism between 2d dimensional affine space and O-border basis scheme by using the results from Chapters 3 and Chapter 4. The techniques from other chapters are applied in Chapter 6.1 to segment border basis schemes and in Chapter 6.2 to O-border basis schemes for which O is of the sawtooth form. KW - Border Bases, Border Basis Scheme, Monomial point, Cotangent Space, Hilbert Schemes KW - Polynomring KW - Basis (Mathematik) KW - Kommutative Algebra, Randbasen, Randbasen Schema Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4702 ER - TY - THES A1 - Fischer, Andreas T1 - An Evaluation Methodology for Virtual Network Embedding N2 - The increasing scale and complexity of computer networks imposes a need for highly flexible management mechanisms. The concept of network virtualization promises to provide this flexibility. Multiple arbitrary virtual networks can be constructed on top of a single substrate network. This allows network operators and service providers to tailor their network topologies to the specific needs of any offered service. However, the assignment of resources proves to be a problem. Each newly defined virtual network must be realized by assigning appropriate physical resources. For a given set of virtual networks, two questions arise: Can all virtual networks be accommodated in the given substrate network? And how should the respective resources be assigned? The underlying problem is commonly known as the Virtual Network Embedding problem. A multitude of algorithms has already been proposed, aiming to provide solutions to that problem under various constraints. For the evaluation of these algorithms typically an empirical approach is adopted, using artificially created random problem instances. However, due to complex effects of random problem generation the obtained results can be hard to interpret correctly. A structured evaluation methodology that can avoid these effects is currently missing. This thesis aims to fill that gap. Based on a thorough understanding of the problem itself, the effects of random problem generation are highlighted. A new simulation architecture is defined, increasing the flexibility for experimentation with embedding algorithms. A novel way of generating embedding problems is presented which migitates the effects of conventional problem generation approaches. An evaluation using these newly defined concepts demonstrates how new insights on algorithm behavior can be gained. The proposed concepts support experimenters in obtaining more precise and tangible evaluation data for embedding algorithms. KW - Virtual Network Embedding KW - Empirical Evaluation KW - Network Virtualization KW - Experimental Algorithmics KW - Virtuelles Netz KW - Virtualisierung KW - Algorithmus KW - Virtuelles Netz KW - Kombinatorische Einbettung Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4793 ER - TY - THES A1 - Löwe, Stefan T1 - Effective Approaches to Abstraction Refinement for Automatic Software Verification N2 - This thesis presents various techniques that aim at enabling more effective and more efficient approaches for automatic software verification. After a brief motivation why automatic software verification is getting ever more relevant, we continue with detailing the formalism used in this thesis and on the concepts it is built on. We then describe the design and implementation of the value analysis, an analysis for automatic software verification that tracks state information concretely. From a thorough evaluation based on well over 4 000 verification tasks from the latest edition of the International Competition on Software Verification (SV-COMP), we learn that this plain value analysis leads to an efficient verification process for many verification tasks, but at the same time, fails to solve other verification tasks due to state-space explosion. From this insight we infer that some form of abstraction technique must be added to the value analysis in order to also allow the successful verification of large and complex verification tasks. As a solution, we propose to incorporate counterexample-guided abstraction refinement (CEGAR) and interpolation into the value domain. To this end, we design a novel interpolation procedure, that extracts from infeasible counterexamples interpolants for the value domain, allowing to form a precision strong enough to exclude these infeasible counterexamples, and to make progress in the CEGAR loop. We then describe several optimizations and extensions to these concepts, such that the value analysis with CEGAR becomes competitive for automatic software verification. As the next step, we combine the value analysis with CEGAR with a predicate analysis, to obtain a more precise and efficient composite analysis based on CEGAR. This composite analysis is indeed on a par with the world’s leading software verification tools, as witnessed by the results of SV-COMP’13 where this approach achieved the 2 nd place in the overall ranking. After having available competitive CEGAR-based analyses for the value domain, the predicate domain, and the combination thereof, we then turn our attention to techniques that have the goal to make all these CEGAR-based approaches more successful. Our first novel idea in this regard is based on the concept of infeasible sliced prefixes, which allow the computation of different precisions from a single infeasible counterexample. This adds choice to the CEGAR loop, while without this enhancement, no choice for a specific precision, i. e., a specific refinement, is possible. In our evaluation we show, for both the value analysis and the predicate analysis, that choosing different infeasible sliced prefixes during the refinement step leads to major differences in verification effectiveness and verification efficiency. Extending on the concept of infeasible sliced prefixes, we define several heuristics in order to precisely select a single refinement from a set of possible refinements. We make this new concept, which we refer to as guided refinement selection, available to both the value and predicate analysis, and in a large-scale evaluation we try to answer the question which selection technique leads to well suited abstractions and thus, to a more effective verification process. Additionally, we present the idea of inter-analysis refinement selection, where the refinement component of a composite analysis may decide which of its component analyses is best to be refined, and in yet another evaluation we highlight the positive effects of this technique. Finally, we present the results of SV-COMP’16, where the verifier we contributed and which is based on the concepts and ideas presented in this thesis achieved the 1 st place in the category DeviceDriversLinux64. KW - software verification, model checking, counterexample guided abstraction refinement, CEGAR, interpolation, sliced prefixes, refinement selection, value analysis, predicate analysis, CPAchecker, automatic, automated KW - Programmverifikation Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4815 ER - TY - THES A1 - Rosenthal, Kristina T1 - Die Tits-Alternative für eine relevante Klasse endlich präsentierter Gruppen unter besonderer Berücksichtigung computeralgebraischer Aspekte T1 - The Tits alternative for a relevant class of finitely presented groups in special consideration of symbolic computational aspects N2 - Eine Gruppe erfüllt die Tits-Alternative, wenn sie entweder eine nicht-abelsche freie Untergruppe vom Rang 2 enthält oder virtuell auflösbar ist, d. h. eine auflösbare Untergruppe von endlichem Index enthält. Diese Eigenschaft geht auf J. Tits zurück, der sie für endlich erzeugte lineare Gruppen nachwies. Es wird eine relevante Klasse endlich präsentierter Gruppen in Bezug auf die Tits-Alternative untersucht. Die betrachteten Gruppen stellen eine Verallgemeinerung von Pride-Gruppen und der von Vinberg betrachteten Gruppen erzeugt von periodisch gepaarten Relationen für drei Erzeugende dar. Zusätzlich treten diese Gruppen als Fundamentalgruppen hyperbolischer Orbifaltigkeiten auf. Es wird der Nachweis der Tits-Alternative unter bestimmten Voraussetzungen an die Präsentierungen der betrachteten Gruppen erbracht. Für diesen Nachweis werden verschiedene Methoden angewandt: Es werden zum einen homomorphe Bilder der Gruppen betrachtet. Zum anderen wird die Existenz wesentlicher Darstellungen in eine lineare Gruppe nachgewiesen. Basierend auf diesen Darstellungen kann in vielen Fällen der Nachweis der Existenz nicht-abelscher freier Untergruppen erbracht werden. Zusätzlich wird für den Nachweis der Endlichkeit und damit der Tits-Alternative einiger Gruppen eine Methode angewandt, die auf Berechnungen von Gröbner-Basen in nicht-kommutativen Polynomringen basiert. Es wird dabei die Dimension der Gruppenringe betrachtet als Vektorräume berechnet. Für die betrachtete Klasse von Gruppen wird für Relationen der Blocklänge 1 die Tits-Alternative vollständig nachgewiesen. Als Folgerung ergibt sich eine Klassifikation der endlichen unter diesen Gruppen. N2 - A group is said to satisfy the Tits alternative if it contains a non-abelian free subgroup of rank 2 or is virtually solvable, i. e. it contains a solvable subgroup of finite index. This property was established by J. Tits, who proved that it is satisfied by finitely generated linear groups. A relevant class of finitely presented groups is investigated concerning the Tits alternative. These groups are generalizations for the three generator case of the so called Pride groups and the groups defined by periodic paired relations as considered by Vinberg. Furthermore, these groups appear as fundamental groups of hyperbolic orbifolds. The Tits alternative is proved for the considered groups under certain conditions concerning their presentations. Several methods to prove the Tits alternative are used: On the one hand, homomorphic images of the groups are considered. On the other hand, the existence of essential representations in a linear group is proved. Based on these representations, the existence of non-abelian free subgroups is proved in many cases. In addition, a method using Gröbner bases computations in non-commutative polynomial rings is used to prove a group is finite and thus satisfies the Tits alternative. For this purpose, the dimension of the group ring considered as a vector space is investigated. The considered groups with block length 1 are proved to satisfy the Tits alternative. As a conclusion, a classification of the finite considered groups with block length 1 is obtained. KW - Tits-Alternative KW - nicht-kommutative Gröbner-Basis KW - Tits alternative KW - non-commutative Gröbner basis KW - Kombinatorische Gruppentheorie KW - Gröbner-Basis Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-2865 ER - TY - THES A1 - Kurz, Thomas T1 - Adapting Semantic Web Information Retrieval to Multimedia N2 - The amount of audio, video and image data on the Web is immensely growing, which leads to data management problems based on the hidden character of Multimedia. Therefore the interlinking of semantic concepts and media data with the aim to bridge the gap between the Internet of documents and the Web of Data has become a common practice. However, the value of connecting media to its semantic meta data is limited due to lacking access methods and the absence of an adapted query language specialized for media assets and fragments. This thesis aims to extend the standard query language for the Semantic Web (SPARQL) with media specific concepts and functions. The main contributions of the work are an exhaustive survey on Multimedia query languages of the last 3 decades, the SPARQL extension specification itself and an approach for the efficient evaluation of the new query concepts. Additionally I elaborate and evaluate a meta data based media fragment similarity approach, which provides a basis for further language extensions. N2 - Das Wachstum multimedialer Daten wie Audio, Video und Bilder war in den letzten Jahren immens. Das Besondere an dieser Art der Daten ist die versteckte Semantik, die sich nur schwer mit herkömmlichen Information Retrieval Funktionen verbinden lässt und dadurch zu Problemen im Management der Multimedia Daten führt. Konzepte des Semantic Web eignen sich allerdings sehr gut, diese Lücke zu schließen, was sich in vielen Szenarien bereits positiv etabliert hat. Nichtsdestotrotz fehlen mit geeigneten Zugriffsmethoden und einer adaptierten Anfragesprache wichtige Teile, um dieses Konzept der verlinkten Multimedia Daten abzurunden und voll in einem End-to-End Prozess zu verwenden. In dieser Arbeit stelle ich eine Erweiterung der Standard-Anfragesprache im Semantic Web (SPARQL) um multimedia-spezifische Funktionen vor. Der wissenschaftliche Beitrag lässt sich dabei in drei Teile gliedern: Ein umfassendes Survey zu Multimedia Anfragesprachen der letzten 30 Jahre, die Erweiterung von SPARQL inklusive einer geeigneten Methodik zur Anfrageoptimierung, sowie ein Ansatz zur fragment-basierten Ähnlichkeitsberechnung von Bildern mit zugehöriger Evaluierung. KW - SPARQL KW - Semantic Web KW - Multimedia KW - SPARQL KW - Multimedia KW - Semantic Web KW - Web of Data KW - SPARQL-MM Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8276 ER - TY - THES A1 - Planche, Benjamin T1 - Bridging the Realism Gap for CAD-Based Visual Recognition N2 - Computer vision aims at developing algorithms to extract high-level information from images and videos. In the industry, for instance, such algorithms are applied to guide manufacturing robots, to visually monitor plants, or to assist human operators in recognizing specific components. Recent progress in computer vision has been dominated by deep artificial neural network, i.e., machine learning methods simulating the way that information flows in our biological brains, and the way that our neural networks adapt and learn from experience. For these methods to learn how to accurately perform complex visual tasks, large amounts of annotated images are needed. Collecting and labeling such domain-relevant training datasets is, however, a tedious—sometimes impossible—task. Therefore, it has become common practice to leverage pre-available three-dimensional (3D) models instead, to generate synthetic images for the recognition algorithms to be trained on. However, methods optimized over synthetic data usually suffer a significant performance drop when applied to real target images. This is due to the realism gap, i.e., the discrepancies between synthetic and real images (in terms of noise, clutter, etc.). In my work, three main directions were explored to bridge this gap. First, an innovative end-to-end framework is proposed to render realistic depth images from 3D models, as a growing number of solutions (especially in the industry) are utilizing low-cost depth cameras (e.g., Microsoft Kinect and Intel RealSense) for recognition tasks. Based on a thorough study of these devices and the different types of noise impairing them, the proposed framework simulates their inner mechanisms, comprehensively modeling vital factors such as sensor noise, material reflectance, surface geometry, etc. Able to simulate a wide panel of depth sensors and to quickly generate large datasets, this framework is used to train algorithms for various recognition tasks, consistently and significantly enhancing their performance compared to other state-of-the-art simulation tools. In some cases, however, relevant 2D or 3D object representations to generate synthetic samples are not available. Considering this different case of data scarcity, a solution is then proposed to incrementally build a representation of visual scenes from partial observations. Provided observations are localized from one to another based on their content and registered in a global memory with spatial properties. Simultaneously, this memory can be queried to render novel views of the scene. Furthermore, unobserved regions can be hallucinated in memory, in consistence with previous observations, hallucinations, and global priors. The efficacy of the proposed mnemonic and generative system, trainable end-to-end, is demonstrated on various 2D and 3D use-cases. Finally, an advanced convolutional neural network pipeline is introduced, tackling the realism gap from a novel angle. While most methods addressing this problem focus on bringing synthetic samples—or the knowledge acquired from them—closer to the real target domain, the proposed solution performs the opposite process, mapping unseen target images into controlled synthetic domains. The pre-processed samples can then be handed to downstream recognition methods, themselves purely trained on similar synthetic data, to greatly improve their accuracy. For each approach, a variety of qualitative and quantitative studies are detailed, providing successful comparisons to state-of-the-art methods. By proposing solutions to bridge the realism gap from either side, as well as a pipeline to improve the acquisition and generation of new visual content, this thesis provides a unique perspective on the challenges of data scarcity when building robust recognition systems. N2 - Die Computer Vision strebt an, Algorithmen zum Extrahieren hochwertiger Informationen von Bildern und Videos zu entwickeln. In der Industrie werden solche Algorithmen beispielsweise angewendet, um Fertigungsroboter zu steuern, um Betriebe visuell zu überwachen, oder um Mitarbeiter bei der Erkennung bestimmter Komponenten zu unterstützen. Die kürzlichen Fortschritte im Bereich Computer Vision wurden von tiefen künstlichen neuronalen Netzen dominiert. Diese Methoden des maschinelles Lernens (Machine Learning) simulieren die Art und Weise, in der die Information in unseren biologischen Gehirnen verarbeitet wird und in der unsere neuronale Netze sich anpassen und aus Erfahrung lernen. Damit diese Methoden zur genauen Ausführung komplexer visueller Aufgaben befähigt werden, müssen sie mit einer großen Anzahl von annotierten Bildern trainiert werden. Die Erhebung und Kennzeichnung entsprechender Trainingsdatensätze ist jedoch eine langwierige und manchmal sogar unmögliche Aufgabe. Deswegen ist es zur gängigen Praxis geworden, stattdessen die vorhandenen 3D-Modelle zur Generierung synthetischer Bilder einzusetzen, damit die Erkennungsalgorithmen mit Hilfe dieser Bilder trainiert werden. Allerdings, bei der Anwendung auf die realen Zielbilder, erleiden die Methoden, die durch synthetische Daten angepasst wurden, einen erheblichen Leistungsabfall. Dies geschieht aufgrund der Realismuslücke (Realism Gap), das heißt durch die Diskrepanzen zwischen synthetischen und realen Bildern (hinsichtlich von Rauschen, Störungen usw.). In meiner Arbeit wurden drei Hauptrichtungen untersucht, um diese Lücke zu schließen. Zuerst wird ein innovatives End-to-End-Framework vorgeschlagen, um realistische Tiefenbilder von 3D-Modellen zu rendern, denn immer mehr Lösungen (insbesondere in der Industrie) verwenden kostengünstige Tiefen-Kameras (z. B. Microsoft Kinect und Intel RealSense) für die Erkennungsaufgaben. Aufgrund einer gründlichen Untersuchung dieser Geräte und der verschiedenen Arten von Rauschen, die dem Aufnahmen beeinträchtigen, simuliert das vorgeschlagene Framework deren innere Mechanismen, indem Schlüsselfaktoren wie Sensorrauschen, Reflektionsgrade der Materialien, Oberflächengeometrie usw. umfassend modelliert werden. Dieses Framework ist in der Lage eine breite Palette von Tiefensensoren zu simulieren und schnell große Datensätze zu generieren. Dies wird eingesetzt, um die Algorithmen für verschiedene Erkennungsaufgaben zu trainieren und deren Leistung im Vergleich zu anderen hochmodernen Simulationsmethoden konsistent und erheblich zu verbessern. In manchen Fällen sind jedoch keine relevanten 2D- oder 3D-Objektdarstellungen zur Erzeugung von synthetischen Bildern verfügbar. Ausgehend von dieser Problematik des Datenmangels wurde eine Lösung vorgeschlagen, in der die Rekonstruktion von visuellen Szenen aus Teilbeobachtungen schrittweise durchgeführt wird. Die Bilder werden anhand ihres Inhalts in Bezug zueinander lokalisiert und in einer globalen Gedächtnisstruktur mit räumlichen Eigenschaften registriert Gleichzeitig kann dieses Gedächtnis abgerufen werden, um neuen Ansichten der Szene zu rendern. Darüber hinaus können bisher unbeobachtete Regionen in Übereinstimmung mit früheren Beobachtungen, Halluzinationen und globalen Vorwissen im Gedächtnis halluziniert werden. Die Wirksamkeit des vorgeschlagenen, durchgehend trainierbaren mnemonischen und generativen Systems, wird anhand von verschiedenen 2D- und 3D-Anwendungsfällen demonstriert. Schließlich wird eine auf Convolutional Neural Networks (CNNs) basierte weiter entwickelte Pipeline vorgestellt, die die Realismuslücke aus einem neuen Blickwinkel angeht. Während die meisten Methoden, die sich mit diesem Problem befassen, sich darauf konzentrieren, synthetische Datenproben (bzw. daraus erworbenes Wissen) näher an die echte/reale Zieldomäne zu bringen, führt die vorgeschlagene Lösung den umgekehrten Prozess durch, indem ungesehene Zielbilder in den kontrollierten synthetischen Domänen abgebildet werden. Die vorbehandelten Datenproben können dann für die nachgeschalteten Erkennungsalgorithmen übergeben werden, die selbst anhand der ähnlichen synthetischen Daten trainiert wurden, um deren Genauigkeit deutlich zu verbessern. Für jeden Ansatz werden verschiedene qualitative und quantitative Studien durchgeführt, um mit sie den neuesten Methoden zu vergleichen. Insgesamt werden in dieser Arbeit Methoden zur Überbrückung der Realismuslücke auf beiden Seiten sowie eine Lösung zur Verbesserung der Erfassung und Generierung neuer visueller Inhalte beschrieben. Daher bietet diese Dissertation eine neuartige Perspektive auf die Herausforderungen der Datenknappheit bei der Entwicklung robuster Erkennungssysteme. KW - computer vision KW - machine learning KW - domain adaptation KW - realism gap KW - visual understanding Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8361 ER - TY - THES A1 - Fink, Thomas T1 - Curvature Detection by Integral Transforms N2 - In various fields of image analysis, determining the precise geometry of occurrent edges, e.g. the contour of an object, is a crucial task. Especially the curvature of an edge is of great practical relevance. In this thesis, we develop different methods to detect a variety of edge features, among them the curvature. We first examine the properties of the parabolic Radon transform and show that it can be used to detect the edge curvature, as the smoothness of the parabolic Radon transform changes when the parabola is tangential to an edge and also, when additionally the curvature of the parabola coincides with the edge curvature. By subsequently introducing a parabolic Fourier transform and establishing a precise relation between the smoothness of a certain class of functions and the decay of the Fourier transform, we show that the smoothness result for the parabolic Radon transform can be translated into a change of the decay rate of the parabolic Fourier transform. Furthermore, we introduce an extension of the continuous shearlet transform which additionally utilizes shears of higher order. This extension, called the Taylorlet transform, allows for a detection of the position and orientation, as well as the curvature and other higher order geometric information of edges. We introduce novel vanishing moment conditions which enable a more robust detection of the geometric edge features and examine two different constructions for Taylorlets. Lastly, we translate the results of the Taylorlet transform in R^2 into R^3 and thereby allow for the analysis of the geometry of object surfaces. KW - Curvature KW - Wavelet KW - Shearlet KW - Parabolic Radon transform KW - Edge classification KW - Krümmung KW - Wavelet-Transformation KW - Shearlet KW - Radon-Transformation KW - Konturfindung Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-7684 ER - TY - THES A1 - Lucas, Yvan T1 - Credit card fraud detection using machine learning with integration of contextual knowledge N2 - We have proposed a strategy for the creation of attributes based on hidden Markov models (HMM) characterizing the transaction from different points of view. This strategy makes it possible to integrate a broad spectrum of sequential information into the attributes of transactions. In fact, we model the authentic and fraudulent behavior of merchants and card holders according to two univariate characteristics: the date and the amount of transactions. In addition, attributes based on HMMs are created in a supervised manner, thereby reducing the need for expert knowledge for the creation of the fraud detection system. Ultimately, our HMM-based multi-perspective approach allows automated data pre-processing to model time correlations to complement and eventually replace transaction aggregation strategies to improve detection efficiency. Experiments carried out on a large set of credit card transaction data from the real world (46 million transactions carried out by Belgian card holders between March and May 2015) have shown that the strategy proposed for data preprocessing based on HMM can detect more fraudulent transactions when combined with the strategy of preprocessing reference data based on expert knowledge for the detection of credit card fraud. KW - Kreditkartenmissbrauch KW - Maschinelles Lernen Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-7713 ER - TY - THES A1 - Ansah, Frimpong T1 - Performance and optimization technologies for software defined industrial networks N2 - The concept of programmable networks is radically changing the way communication infrastructures are designed, integrated, and operated. Currently, the topic is spearheaded by concepts such as software-defined networking, forwarding and control element separation, and network function virtualization. Notably, software-defined networking has attracted significant attention in telecommunication and data centers and thus already in some production-grade networks. Despite the prevalence of software-defined networking in these domains, industrial networks are yet to see its benefits to encourage adoption. However, the misconceptions around the concept itself, the role of virtualization, and algorithms pose a significant obstacle. Furthermore, the desire to accommodate new services in the automation industry results in a pattern of constantly increasing complexity of industrial networks, which is compounded by the requirement to provide stringent deterministic service guarantees considering characteristically different applications and thus posing a significant challenge for management, configuration, and maintenance as existing solutions are architecturally inflexible. Therefore, the first contribution of this thesis addresses the misconceptions around software-defined networking by providing a comparative analysis of programmable network concepts, detailing where software-defined networks compare with other concepts and how its principles can be leveraged to evolve industrial networks. Armed with the fundamental principles of programmable networks, the second contribution identifies virtualization technologies and proposes novel algorithms to provide varied quality of service guarantees on converged time-sensitive Ethernet networks using software-defined networking concepts. Finally, a performance analysis of a software-defined hybrid deployment solution for control and management of time-sensitive Ethernet networks that integrates proposed novel algorithms is presented as an industrial use-case that enables industrial operators to harness the full potential of time-sensitive networks. KW - Performance KW - Software Defined Industrial Networks KW - Virtual Network Embedding KW - Schedulability Analysis KW - Worst-case Delay Analysis KW - Software Defined Industrial Networks KW - Deterministic Petri-net and Queuing networks KW - Virtual Network Embedding and Worst-case Delay Analysis KW - Schedulability Analysis KW - Performance Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-9002 PB - Universität Passau CY - Passau ER - TY - THES A1 - Charpenay, Victor T1 - Semantics for the Web of Things: Modeling the Physical World as a Collection of Things and Reasoning with their Descriptions N2 - The main research question of this thesis is to develop a theory that would provide foundations for the development of Web of Things (WoT) systems. A theory for WoT shall provide a model of the ‘things’ WoT agents relate to such that these relations determine what interactions take place between these agents. This thesis presents a knowledge-based approach in which the semantics of WoT systems is given by a transformation (an homomorphism) between a graph representing agent interactions and a knowledge graph describing ‘things’. It focuses on three aspects of knowledge graphs in particular: the vocabulary with which assertions can be made, the rules that can be defined over this vocabulary and its serialization to efficiently exchange pieces of a knowledge graph. Each aspect is developed in a dedicated chapter, with specific contributions to the state-of-the-art. The need for a unified vocabulary to describe ‘things’ in WoT and the Internet of Things (IoT) has been identified early on in the literature. Many proposals have been consequently published, in the form of Web ontologies. In Ch. 2, a systematic review of these proposals is being developed, as well as a comparison with the data models of the principal IoT frameworks and protocols. The contribution of the thesis in that respect is an alignment between the Thing Description (TD) model and the Semantic Sensor Network (SSN) ontology, two standards of the World Wide Web Consortium (W3C). The scope of this thesis is generally limited to Web standards, especially those defined by the Resource Description framework (RDF). Web ontologies do not only expose a vocabulary but also rules to extend a knowledge graph by means of reasoning. Starting from a set of TD documents, new relations between ‘things’ can be “discovered” this way, indicating possible interactions between the servients that relate to them. The experiments presented in Ch. 3 were done on the basis of this semantic discovery framework on two use cases: a building automation use case provided by Intel Labs and an industrial control use case developed internally at Siemens. The relations to discover often involve anonymous nodes in the knowledge graph: the chapter also introduces a novel skolemization algorithm to correctly process these nodes on a well-defined fragment of the Web Ontology Language (OWL). Finally, because this semantic discovery framework relies on the exchange of TD documents, Ch. 4 introduces a binary format for RDF that proves efficient in serializing TD assertions such that even the smallest WoT agents, i.e. micro-controllers, can store and process them. A formalization for the semantics-preserving compaction and querying of TD documents is also introduced in this chapter, at the basis of an embedded RDF store called the µRDF store. The ability of all WoT agents to query logical assertions about themselves and their environment, as found in TD documents, is a first step towards knowledge-based intelligent systems that can operate autonomously and dynamically in a decentralized way. The µRDF store is an attempt to illustrate the practical outcomes of the theory of WoT developed throughout this thesis. N2 - Die Dissertation entwickelt eine theoretische Grundlage für die Spezifikation Web of Things (WoT)-Systemen. Die Spezifikation der WoT-Systeme basiert auf einem Modell für die Dinge, oder Things, mit denen WoT-Agenten Beziehungen schaffen, welche Interaktionen zwischen Agenten erlauben. Diese Dissertation stellt einen wissensbasierten Ansatz vor, in dem die Semantik von WoT-Systemen als eine Transformation von einem Graphen von Agenten-Interaktionen nach einem Knowledge Graph definiert ist. Diese Arbeit deckt genau drei Aspekte Knowledge Graphs ab: das Vokabular, mit dem logische Schlüsse formuliert werden, die Regeln, die auf einem Vokabular basieren können und Serialisierung, um den effizienten Austausch zwischen Teilen eines Knowledge Graph zu ermöglichen. Alle drei Aspekt werden mit ihren wissenschaftlichen Beitrag in einem eigenen Kapitel adressiert. Der Bedarf an einem vereinigten Vokabular, um im WoT und dem Internet of Things (IoT) Things zu beschreiben, wurden in der Literatur frühzeitig identifiziert. Viele Ansatze wurden diesbezüglich vor allem als Web Ontologien veröffentlicht. Im Kapitel 2 werden diese Ansätze miteinander, sowie mit Datenmodelle dominierender IoT-Frameworks und Protokolle verglichen. Der Beitrag der Dissertation diesbezüglich ist die Verschmelzung des WoT Thing Description (TD) Modells und der Semantic Sensor Network (SSN) Ontologie, zwei vom World Wide Web Consortium (W3C) veröffentlichte Standards, in eine einzige Ontologie. Der Rahmen dieser Dissertation wird auf Web Standards begrenzt, insbesondere im Resource Description Framework (RDF) enthaltenen Standards. Web Ontologien bestehen nicht nur aus einm Vokabular, sondern auch aus Regel, um einen Knowledge Graphen durch Inferenz zu erweitern. Anhand einer Menge von TD-Dokumenten können neue Beziehungen zwischen Things abgeleitet werden und dadurch neue Interaktionen zwischen denjenigen Agenten, die sich auf diese Things beziehen eingeführt werden. Die im Kapitel 3 beschriebenen Experimente setzen dieses semantische Framework in zwei Domäne um: Gebäudeautomatisierung und Industrielle Kontrollsysteme. Das Erkennen impliziter Beziehungen zwischen Things hängt in bestimmten Fällen von sogenannten anonymen Knoten im Graphen ab: das Kapitel führt einen neuen Skolemization Algorithmus ein, um diese Knoten für einen bestimmten Teil der Web Ontology Language (OWL) korrekt zu verarbeiten. Zum Schluss, da die Umsetzung dieses semantischen Frameworks den Austausch von TD-Dokumenten erfordert, wird im Kapitel 4 ein binäres Format für RDF eingeführt, welches sich als sehr effizient für die Serialisierung erweist, damit auch kleine WoT Agenten, nämlich Mikrocontroller, TD-Dokumente speichern und verarbeiten können. Eine formale Definition für die Verdichtung und die Abfrage von TD-Dokumenten wird in diesem Kapitel eingeführt. Das Kapitel beschreibt auch die Implementierung einer eingebetteten RDF Datenbank, die µRDF Store genannt wurde. Die Fähigkeit WoT-Agenten logische Schlüsse über sich selbst und ihre Umgebung zu ziehen ist der erste Schritt in Richtung eines wissensbasierten intelligenten Systems, das autonom, dynamisch und dezentral agieren kann. Der µRDF Store zeigt die praktischen Vorteile, der in dieser Dissertation entwickelten Theorie für WoT auf. KW - Semantic Web KW - Web of Things KW - Internet of Things KW - Thing Description KW - Web Ontologies KW - Semantic Web KW - Internet der Dinge Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-7578 ER - TY - THES A1 - Berndl, Emanuel T1 - Embedding a Multimedia Metadata Model into a Workflow-driven Environment Using Idiomatic Semantic Web Technologies N2 - The Semantic Web exists for about 20 years by now, but its applicability as well as its presence does not live up to the standards of its original idea. Incorporated Semantic Web Technologies do have an initial barrier to learn and apply, which can discourage many potential users. This leads to less available data overall in addition to decreased data quality. This work solves parts of the aforementioned problem by supporting idiomatic entry to those Semantic Web Technologies, allowing for "easier" accessibility and usability. Anno4j is a Java library that implements a form of Object-Relational Mapping for RDF data. With its application, RDF data can be created via a mapping by simply instantiating Java objects - an object-oriented programming concept the user is familiar with. On the other side, requesting persisted data is supported by a path-based querying possibility, while other features like transactional behaviour, code generation, and automated validation of input contribute to a more effective, comprehensive, and straightforward usage. A use-case is provided by the MICO Platform, a centralized software instance that connects autonomous multimedia extractors in a workflow-driven fashion. This leads to a rich metadata background for the inserted multimedia files, enabling them to be used in diverse scenarios as well as unlocking yet hidden semantics. For this task it was necessary to design and implement a metadata model that is able to aggregate and merge the varying extractor results under a common denominator: the MICO Metadata Model. The results of this work allow the use case to incorporate idiomatic Semantic Web Technologies which are then usable natively by non-Semantic Web experts. Additionally, an increase has been achieved in forms of data integration, synchronisation, integrity and validity, as well as an overall more comprehensive and rich implementation of the multimedia extractors. KW - Semantic Web KW - Multimedia KW - Workflows KW - Multimedia KW - Metadaten KW - RDF KW - Semantic Web Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-6708 ER - TY - THES A1 - Kolesnikov, Sergiy T1 - Feature Interactions in Configurable Software Systems N2 - Software has become an important part of our life. Therefore, the number of different applications scenarios and user requirements of software systems grows rapidly. To satisfy these requirements, software vendors build configurable software systems that can be tailored to diverse needs without rebuilding them from scratch, which reduces costs and development time. Despite considerable advances in software engineering, which allow building high-quality configurable software systems, some challenges remain. One of these challenges is the feature interaction problem that arises when parts (features), from which a configurable system is composed, interact in unexpected ways, and inadvertently change the behavior or quality attributes (such as performance) of the system. The goal of this dissertation is to systematically study the nature of feature interactions, their causes, their influence on performance of configurable systems, and, based on empirical results, suggest ways of improving techniques for detecting and predicting feature interactions. More specifically, we compared and evaluated different strategies for the analysis of configurable software systems. The results of our evaluation complement empirical data from previous work about how different analysis strategies for configurable software systems compare with respect to different aspects, such as performance. These results shall be used to develop effective and scalable techniques and tools for analysis of configurable software including feature-interaction detection and prediction techniques and tools. Technically, we used a machine-learning technique to quantify the influence of feature interactions on performance of real-world configurable systems. We studied the characteristics of interactions that have the largest influence on performance and found that interactions among few features have higher influence than interactions among many features. With a growing number of interacting features, the influence of the corresponding interactions decreases consistently. This implies that interactions involving multiple features can be ignored in practice because of their marginal influence on performance. We also investigated the causes of the interactions and were able to identify several patterns that link these interactions to the architecture of the systems: For example, we found that if a data processing system consisted of multiple features that processed the same data in sequence then these features interacted. The identified patterns can help to anticipate performance interactions already at an early development stage when a system’s architecture is designed. Furthermore, considering that control-flow interactions (observable at the level of control flow among features) are easier to detect than performance interactions (externally observable through measuring performance of different combinations of features), we conducted a case study on two configurable systems. In this case study, we investigated a possible relation among control-flow feature interactions and performance feature interactions. We also discussed how this relation can be exploited by interaction detection and performance prediction techniques to make them more time efficient and precise. Our case study on two real-world configurable systems revealed that a relation indeed exists, and we were able to show how it can be used to reduce the search space of possibly existing performance interactions. The study can serve as a blueprint for further studies that can rely on our conceptual framework for investigating relations among external and internal interactions. Overall, the contribution of this dissertation consists of scientific and technical insights, practical tool implementations, empirical evaluations, and case studies that advance the current state of research in the area of feature interactions in configurable software systems. In particular, we provide insights into the causes of feature interactions and their influence on performance of real-world configurable systems (e.g., interaction patterns, decreasing influence of interactions with growing number of involved features). Our results also suggest ways of improving techniques for detecting and predicting feature interactions (e.g., ignoring interactions among multiple features, reducing the search space based on relations among interactions). KW - Configurable software system KW - Feature interaction KW - Performance influence model KW - Software product line KW - Variability-aware software analysis strategy KW - Softwareentwicklung KW - Qualitätssicherung Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-6739 ER - TY - THES A1 - Stahlbauer, Andreas T1 - Abstract Transducers for Software Analysis and Verification N2 - Whenever software faults can endanger human life, property, or the environment, the absence of faults must be ensured with utmost care and the best technologies available. Evidence is needed showing that all requirements are satisfied and that the risk of faults is reduced. One technique to conduct such a verification task—composed of the software to verify, the specification to check, and a model of the environment—is software model checking. To conduct a verification task with a model checker, different models of the task are constructed. We distinguish between two types of task models: syntactic task models and semantic task models, which define the respective syntactic structure (control flow) and semantic structure (state transitions, invariants) of the verification task. When constructing such models, we can observe that similar structures and substructures reappear within and among different verification tasks. For example, the same assertions to check can appear in different functions, or the same predicate can be part of different invariants to describe sets of program states. Similarities that appear during the model construction process can be the result of solving similar reasoning problems, often solved using computationally expensive procedures (as typical for model checking), over and over again. Not reusing results of solving similar problems, not having a means for conducting repeated efforts automatically, or not trying to reduce the number of similar reasoning efforts, is a waste of precious resources. To address these problems, we present a common conceptual and technical foundation for sharing syntactic and semantic task artifacts for reuse, within and among verification runs. Both the syntactic construction of a verification task and the construction of its semantic model—which describes all possible behaviors and states—are covered. We study how commonalities and regularities in the task models can be taken into account to facilitate the process of sharing task artifacts for reuse, and to make the overall verification process more efficient and effective. We introduce abstract transducers as the theoretical foundation of this thesis: a type of finite-state transducers with an inherent notion of abstraction for states, the input alphabet, and its output alphabet. Abstracting these transducers allows us to widen both the set of input words for that they produce output and the sets of output words. Abstract transducers are instantiated as task artifact transducers to map from program structures to task artifacts to share. We show that the notion of abstraction provides a means for increasing the scope for that task artifacts are shared for reuse. We present two instances of task artifact transducers: Yarn transducers and precision transducers. We use Yarn transducers for providing code to weave into the control-flow structure of a computer program, and present the Loom analysis as a means for orchestrating the weaving process. Precision transducers provide a means for sharing abstraction precisions for reuse, thus aid in defining the level of abstraction of a semantic task model. For both types of transducers, we provide empirical evidence on their practical applicability, for example, to verify Linux kernel modules, and show that they can help in increasing the verification performance. KW - Program Analysis KW - Software Model Checking KW - Automata Theory KW - Transduktor KW - Formale Beschreibungstechnik KW - Modellgetriebene Entwicklung Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8468 ER - TY - THES A1 - Garchery, Mathieu T1 - User-centered intrusion detection using heterogeneous data N2 - With the frequency and impact of data breaches raising, it has become essential for organizations to automate intrusion detection via machine learning solutions. This generally comes with numerous challenges, among others high class imbalance, changing target concepts and difficulties to conduct sound evaluation. In this thesis, we adopt a user-centered anomaly detection perspective to address selected challenges of intrusion detection, through a real-world use case in the identity and access management (IAM) domain. In addition to the previous challenges, salient properties of this particular problem are high relevance of categorical data, limited feature availability and total absence of ground truth. First, we ask how to apply anomaly detection to IAM audit logs containing a restricted set of mixed (i.e. numeric and categorical) attributes. Then, we inquire how anomalous user behavior can be separated from normality, and this separation evaluated without ground truth. Finally, we examine how the lack of audit data can be alleviated in two complementary settings. On the one hand, we ask how to cope with users without relevant activity history ("cold start" problem). On the other hand, we seek how to extend audit data collection with heterogeneous attributes (i.e. categorical, graph and text) to improve insider threat detection. After aggregating IAM audit data into sessions, we introduce and compare general anomaly detection methods for mixed data to a user identification approach, designed to learn the distinction between normal and malicious user behavior. We find that user identification outperforms general anomaly detection and is effective against masquerades. An additional clustering step allows to reduce false positives among similar users. However, user identification is not effective against insider threats. Furthermore, results suggest that the current scope of our audit data collection should be extended. In order to tackle the "cold start" problem, we adopt a zero-shot learning approach. Focusing on the CERT insider threat use case, we extend an intrusion detection system by integrating user relations to organizational entities (like assignments to projects or teams) in order to better estimate user behavior and improve intrusion detection performance. Results show that this approach is effective in two realistic scenarios. Finally, to support additional sources of audit data for insider threat detection, we propose a method representing audit events as graph edges with heterogeneous attributes. By performing detection at fine-grained level, this approach advantageously improves anomaly traceability while reducing the need for aggregation and feature engineering. Our results show that this method is effective to find intrusions in authentication and email logs. Overall, our work suggests that masquerades and insider threats call for different detection methods. For masquerades, user identification is a promising approach. To find malicious insiders, graph features representing user context and relations to other entities can be informative. This opens the door for tighter coupling of intrusion detection with user identities, roles and privileges used in IAM solutions. KW - Anomalie KW - Authenitifikation KW - Computersicherheit Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8704 ER - TY - THES A1 - Koop, Martin T1 - Preventing the Leakage of Privacy Sensitive User Data on the Web N2 - Das Aufzeichnen der Internetaktivität ist mit der Verknüpfung persönlicher Daten zu einer Schlüsselressource für viele kostenpflichtige und kostenfreie Dienste im Web geworden. Diese Dienste sind zum einen Webanwendungen, wie beispielsweise die von Google bereitgestellten Karten/Navigation oder Websuche, die täglich kostenlos verwendet werden. Zum anderen sind es alle Webseiten, die meist kostenlos Nachrichten oder allgemeine Informationen zu verschiedenen Themen bereitstellen. Durch das Aufrufen und die Nutzung dieser Webdienste werden alle Informationen, die im Webdienst verarbeitet werden, an den Dienstanbieter weitergeben. Dies umfasst nicht nur die im Benutzerkonto des Webdienstes gespeicherte Profildaten wie Name oder Adresse, sondern auch die Aktivität mit dem Webdienst wie das anklicken von Links oder die Verweildauer. Darüber hinaus gibt es jedoch auch unzählige Drittparteien, welche zumeist im Hintergrund in die Webdienste eingebunden sind und das Benutzerverhalten der kompletten Webaktivität - Webseiten übergreifend - mitspeichern sowie auswerten. Der Einsatz verschiedener, in der Regel für den Benutzer verborgener Techniken, dient dazu das Online-Verhalten der Benutzer genau zu verfolgen und viele sensible Daten zu sammeln. Dieses Verhalten wird als Web-Tracking bezeichnet und wird hauptsächlich von Werbeunternehmen genutzt. Die gesammelten Daten sind oft personenbezogen und eine wertvolle Ressourcen der Unternehmen, um Beispielsweise passend zum Benutzerprofil personalisierte Werbung schalten zu können. Mit der Nutzung dieser personenbezogenen Daten entstehen aber auch weitreichendere Auswirkungen, welche sich unter anderem in Preisanpassungen für Benutzer mit speziellen Profilattributen, wie der Nutzung von teuren Endgeräten, widerspiegeln. Ziel dieser Arbeit ist es die Privatsphäre der Nutzer im Internet zu steigern und die Nutzerverfolgung von Web-Tracking signifikant zu reduzieren. Dabei stellen sich vier Herausforderungen, die jeweils einen Forschungsschwerpunkt dieser Arbeit bilden: (1) Systematische Analyse und Einordnung eingesetzter Tracking-Techniken, (2) Untersuchung vorhandener Schutzmechanismen und deren Schwachstellen,(3) Konzeption einer Referenzarchitektur zum Schutz vor Web-Tracking und (4) Entwurf einer automatisierten Testumgebungen unter Realbedingungen, um die Reduzierung von Web-Tracking in den entwickelten Schutzmaßnahmen zu untersuchen. Jeder dieser Forschungsschwerpunkte stellt neue Beiträge bereit, um einheitlich das übergeordnete Ziel zu erreichen: der Entwicklung von Schutzmaßnahmen gegen die Preisgabe sensibler Benutzerdaten im Internet. Der erste wissenschaftliche Beitrag dieser Dissertation ist eine umfassende Evaluation eingesetzter Web-Tracking Techniken und Methoden, sowie deren Gefahren, Risiken und Implikationen für die Privatsphäre der Internetnutzer. Die Evaluation beinhaltet zusätzlich die Untersuchung vorhandener Tracking-Schutzmechanismen und deren Schwachstellen. Die gewonnenen Erkenntnisse sind maßgeblich für die in dieser Arbeit neu entwickelten Ansätze und verbessern den bisherigen nicht hinreichend gewährleisteten Schutz vor Web-Tracking. Der zweite wissenschaftliche Beitrag ist die Entwicklung einer robusten Klassifizierung von Web-Tracking, der Entwurf einer effizienten Architektur zur Langzeituntersuchung von Web-Tracking sowie einer interaktiven Visualisierung des Auftreten von Web-Tracking im Internet. Dabei basiert der neue Klassifizierungsansatz, um Tracking zu identifizieren, auf der Entropie Messung des Informationsgehalts von Cookies. Die Resultate der Web-Tracking Langzeitstudien sind unter anderem 1.209 identifizierte Tracking-Domains auf den meistbesuchten Webseiten in Deutschland. Hierbei wurden innerhalb der Top 25 Webseiten im Durchschnitt 45 Tracking-Elemente pro Webseite gefunden. Der Tracker mit dem höchsten Potenzial zum Erstellen eines Benutzerprofils war doubleclick.com, da er 90% der Webseiten überwacht. Die Auswertung des untersuchten Tracking-Netzwerks ergab weiterhin einen detaillierten Einblick in die Tracking-Technik mithilfe von Weiterleitungslinks. Dabei haben wir 1,2 Millionen HTTP-Traces von monatelangen Crawls der 50.000 international meistbesuchten Webseiten analysiert. Die Ergebnisse zeigen, dass 11,6% dieser Webseiten HTTP-Redirects, verborgen in Webseiten-Links, zum Tracken verwenden. Dies wird eingesetzt, um den Webseitenverlauf des Benutzers nach dem Klick durch eine Kette von (Tracking-)Servern umzuleiten, welche in der Regel nicht sichtbar sind, bevor das beabsichtigte Link-Ziel geladen wird. In diesem Szenario erfasst der Tracker wertvolle Verbindungs-Metadaten zu Inhalt, Thema oder Benutzerinteressen der Website. Die Visualisierung des Tracking Ökosystem stellen wir in einem interaktiven Open-Source Web-Tool bereit. Der dritte wissenschaftliche Beitrag dieser Dissertation ist die Konzeption von zwei neuartigen Schutzmechanismen gegen Web-Tracking und der Aufbau einer automatisierten Simulationsumgebung unter Realbedingungen, um die Effektivität der Umsetzungen zu verifizieren. Der Fokus liegt auf den beiden meist verwendeten Tracking-Verfahren: Cookies (hierbei wird eine eindeutigen ID auf dem Gerät des Benutzers gespeichert), sowie Browser-Fingerprinting. Letzteres beschreibt eine Methode zum Sammeln einer Vielzahl an Geräteeigenschaften, um den Benutzer eindeutig zu (re- )identifizieren, ohne eine eindeutige ID auf dem Gerät zu speichern. Um die Effektivität der in dieser Arbeit entwickelten Schutzmechanismen vor Web-Tracking zu untersuchen, implementierten und evaluierten wir die Schutzkonzepte direkt im Chromium Browser. Das Ergebnis zeigt eine erfolgreiche Reduzierung von Web-Tracking um 44%. Zusätzlich verbessert das in dieser Arbeit entwickelte Konzept “Site Isolation” den Datenschutz des privaten Browsing-Modus, ermöglicht das Setzen eines manuellen Speicher-Zeitlimits von Cookies und schützt den Browser gegen verschiedene Bedrohungen wie CSRF (Cross-Site Request Forgery) oder CORS (Cross-Origin Ressource Sharing). Site Isolation speichert dabei den Status der lokalen Website in separaten Containern und kann dadurch diverse Tracking-Methoden wie Cookies, lokalStorage oder redirect tracking verhindern. Bei der Auswertung von 1,6 Millionen Webseiten haben wir gezeigt, dass der Tracker doubleclick.com das höchste Potenzial besitzt, den Nutzer zu verfolgen und auf 25% der 40.000 international meistbesuchten Webseiten vertreten ist. Schließlich demonstrieren wir in unserem erweiterten Chromium-Browser einen robusten Browser-Fingerprinting-Schutz. Der Test unseres Prototyps mittels 70.000 Browsersitzungen zeigt, dass unser Browser den Nutzer vor sogenanntem Browser-Fingerprinting Tracking schützt. Im Vergleich zu fünf anderen Browser-Fingerprint-Tools erzielte unser Prototyp die besten Ergebnisse und ist der erste Schutzmechanismus gegen Flash sowie Canvas Fingerprinting. KW - Web Tracking, Cookies, Browser Fingerprinting, Redirects, Site Isolation KW - Datenschutz KW - Computersicherheit KW - Objektverfolgung Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8717 ER - TY - THES A1 - Alshawish, Ali T1 - Risk-based Security Management in Critical Infrastructure Organizations N2 - Critical infrastructure and contemporary business organizations are experiencing an ongoing paradigm shift of business towards more collaboration and agility. On the one hand, this shift seeks to enhance business efficiency, coordinate large-scale distribution operations, and manage complex supply chains. But, on the other hand, it makes traditional security practices such as firewalls and other perimeter defenses insufficient. Therefore, concerns over risks like terrorism, crime, and business revenue loss increasingly impose the need for enhancing and managing security within the boundaries of these systems so that unwanted incidents (e.g., potential intrusions) can still be detected with higher probabilities. To this end, critical infrastructure organizations step up their efforts to investigate new possibilities for actively engaging in situational awareness practices to ensure a high level of persistent monitoring as well as on-site observation. Compliance with security standards is necessary to ensure that organizations meet regulatory requirements mostly shaped by a set of best practices. Nevertheless, it does not necessarily result in a coherent security strategy that considers the different aims and practical constraints of each organization. In this regard, there is an increasingly growing demand for risk-based security management approaches that enable critical infrastructures to focus their efforts on mitigating the risks to which they are exposed. Broadly speaking, security management involves the identification, assessment, and evaluation of long-term (or overall) objectives and interests as well as the means of achieving them. Due to the critical role of such systems, their decision-makers tend to enhance the system resilience against very unpleasant outcomes and severe consequences. That is, they seek to avoid decision options associated with likely extreme risks in the first place. Practically speaking, this risk attitude can significantly influence the decision-making process in such critical organizations. Towards incorporating the aversion to extreme risks into security management decisions, this thesis investigates thoroughly the capabilities of a recently emerged theory of games with payoffs that are probability distributions. Unlike traditional optimization techniques, this theory provides an alternative decision technique that is more robust to extreme risks and uncertainty. Furthermore, this thesis proposes a new method that gives a decision maker more control over the decision-making process through defining loss regions with different importance levels according to people's risk attitudes. In this way, the static decision analysis used in the distribution-valued games is transformed into a dynamic process to adapt to different subjective risk attitudes or account for future changes in the decision caused by a learning process or other changes in the context. Throughout their different parts, this thesis shows how theoretical models, simulation, and risk assessment models can be combined into practical solutions. In this context, it deals with three facets of security management: allocating limited security resources, prioritizing security actions, and tweaking decision making. Finally, the author discusses experiences and limitations distilled from this research and from investigating the new theory of games, which can be taken into account in future approaches. KW - Security Management KW - Game Theory KW - Critical Infrastructures KW - Risk Attitude KW - Uncertainty KW - Spieltheorie KW - Risikomanagement Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-10026 ER - TY - THES A1 - Lang, Thomas T1 - AI-Supported Interactive Segmentation of 3D Volumes N2 - The segmentation of volumetric datasets, i.e., the partitioning of the data into disjoint sub-volumes with the goal to extract information about these regions,is a difficult problem and has been discussed in medical imaging for decades. Due to the ever-increasing imaging capabilities, in particular in X-ray computed tomography (CT) or magnetic resonance imaging, segmentation in industrial applications also gains interest. Especially in industrial applications the generated datasets increase in size. Hence, most applications apply well-known techniques in a 2+1-dimensional manner,i.e., they apply image segmentation procedures on each slice separately and track the progress along the axis of the volume in which the slices are stacked on. This discards the information on preceding or subsequent slices, which is often assumed to be nearly identical. However, in the industrial context this might prove wrong since industrial parts might change their appearance significantly over the course of even a few slices. Moreover, artifacts can further distort the content of the slices. Therefore, three-dimensional processing of voxel volumes has to be preferred, which induces constraints upon the segmentation procedures. For example, they must not consider global information as it is usually not feasible in big scans to compute them efficiently. Yet another frequent problem is that applications focus on individual parts only and algorithms are tailored to that case. Most prominent medical segmentation procedures do so by applying methods to specifically find the liver and only the liver of a patient, for example. The implication is that the same method then cannot be applied to find other parts of the scan and such methods have to be designed individually for any object to be segmented. Flexible segmentation methods are needed too specifically when partitioning unique scans. We define a unique scan to be a voxel dataset for which no comparable volume exists. Classical examples include the use case of cultural heritage where not only the objects themselves are unique but also scan parameters are optimized to obtain the best image quality possible for that specific scan. This thesis aims at introducing novel methods for voxelwise classifications based on local geometric features. The latter are computed from local environments around each voxel and extract information in similar ways as humans do, namely by observing their similarity to geometric or textural primitives. These features serve as the foundation to learning the proposed voxelwise classifiers and to discriminate between segmented and unsegmented voxels. On the one hand, they perform fully automated clustering of volumes for which a representative random sample is extracted first. On the other hand, a set of segmenting classifiers can be trained from few seed voxels, i.e., volume elements for which a domain expert marked if they belong to the components that shall be segmented. The interactive selection offers the advantage that no completely labeled voxel volumes are necessary and hence that unique scans of objects can be segmented for which no comparable scans exist. Overall, it will be shown that all proposed segmentation methods are effectively of linear runtime with respect to the number of voxels in the volume. Thus, voxel volumes without size restrictions can be segmented in an efficient linear pass through the volume. Finally, the segmentation performance is evaluated on selected datasets which shows that the introduced methods can achieve good results on scans from a broad variety of domains for both small and big voxel volumes. N2 - Die Segmentierung von Volumendaten, also die Partitionierung der Daten in disjunkte Teilvolumen zur weiteren Informationsextraktion, ist ein Problem, welches in der medizinischen Bildverarbeitung seit Jahrzehnten behandelt wird. Bedingt durch die sich ständig verbessernden Bilderfassungsmethoden, speziell im Bereich der Röntgen-Computertomographie (CT) oder der Magnetresonanztomographie, gewinnt die Segmentierung von industriellen Volumendaten auch an Wichtigkeit. Insbesondere im industriellen Kontext steigt die Größe der zu segmentierenden Daten jedoch rasant an, so dass sich die meisten Segmentierungsapplikationen auf den 2+1-dimensionalen Fall beschränken, also Bilder verarbeiten und die Ergebnisse über mehrere Bilder hinweg verfolgen. Jedoch werden somit beispielsweise geometrische Informationen über benachbarte Schichten ignoriert. Diese können sich aber gerade im industriellen Bereich signifikant ändern. Aus diesem Grund ist hier die dreidimensionale Bildverarbeitung vorzuziehen. Dadurch ergeben sich neue Einschränkungen, beispielsweise können keine globalen Informationen zur Segmentierung herangezogen werden, da diese typischerweise nicht effizient berechenbar sind. Ferner fokussieren sich dreidimensionale Methoden aus medizinischen Bereichen zumeist auf bestimmte Bestandteile der Daten, wie einzelne Organe. Dies schränkt die Generalität dieser Methoden signifikant ein und somit sind separate Verfahren für jedes zu segmentierende Objekt notwendig. Flexible Methoden sind darüber hinaus bei Anwendung auf einzigartige Scans erforderlich. Ein einzigartiger Scan ist ein Voxelvolumen, für welches kein vergleichbares Datum existiert. Klassische Beispiele sind Kulturgutdigitalisate, da dort nicht nur die Objekte einzigartig sind, sondern auch die Aufnahmeparameter spezifisch für diesen einen Scan optimiert wurden. Die vorliegende Dissertation führt neuartige Methoden zur voxelweisen dreidimensionalen Segmentierung von Volumendaten auf Basis lokaler geometrischer Informationen ein. Die Bewertung dieser Informationen imitiert die menschliche Objektwahrnehmung, indem lokale Regionen mit geometrischen oder strukturellen Primitiven verglichen werden. Mit Hilfe dieser Bewertungen werden voxelweise anzuwendende Klassifikatoren trainiert, welche zwischen erwünschten und unerwünschten Voxeln unterscheiden sollen. Ein Teil dieser Klassifikatoren führt eine vollautomatische Clustering-Analyse durch, nachdem eine repräsentative und zufällig ausgewählte Teilmenge fester Größe an Voxeln selektiert wurde. Die verbliebenen Segmentierungsalgorithmen erhalten Trainingsdaten in Form von Seed-Voxeln, also wenige Volumenelemente, die von einem Domänenexperten markiert wurden. Diese interaktive Herangehensweise ermöglicht das Einbringen von Expertenwissen ohne die Notwendigkeit vollständig annotierter Trainingsvolumen, wodurch auch einzigartige Scans segmentiert werden können. Für alle Verfahren wird dargelegt, dass die eingeführten Algorithmen von asymptotisch linearer Laufzeit in der Anzahl der Voxel im Volumen sind. Somit können Voxeldaten ohne Größenbeschränkungen in einem effizienten linearen Durchgang verarbeitet werden. Abschließend wird die Performanz der vorgestellten Verfahren auf ausgewählten Daten evaluiert und aufgezeigt, dass mit denselben wenigen Verfahren gute Ergebnisse auf vielen unterschiedlichen Domänen und gleichfalls auf kleinen und großen Volumen erzielt werden können. KW - Segmentation KW - Computed Tomography KW - Artificial Intelligence KW - Active Learning KW - Interactive KW - Machine learning KW - Image processing Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-9221 ER - TY - THES A1 - Niedermeier, Michael T1 - Towards High Performability in Advanced Metering Infrastructures N2 - The current movement towards a smart grid serves as a solution to present power grid challenges by introducing numerous monitoring and communication technologies. A dependable, yet timely exchange of data is on the one hand an existential prerequisite to enable Advanced Metering Infrastructure (AMI) services, yet on the other a challenging endeavor, because the increasing complexity of the grid fostered by the combination of Information and Communications Technology (ICT) and utility networks inherently leads to dependability challenges. To be able to counter this dependability degradation, current approaches based on high-reliability hardware or physical redundancy are no longer feasible, as they lead to increased hardware costs or maintenance, if not both. The flexibility of these approaches regarding vendor and regulatory interoperability is also limited. However, a suitable solution to the AMI dependability challenges is also required to maintain certain regulatory-set performance and Quality of Service (QoS) levels. While a part of the challenge is the introduction of ICT into the power grid, it also serves as part of the solution. In this thesis a Network Functions Virtualization (NFV) based approach is proposed, which employs virtualized ICT components serving as a replacement for physical devices. By using virtualization techniques, it is possible to enhance the performability in contrast to hardware based solutions through the usage of virtual replacements of processes that would otherwise require dedicated hardware. This approach offers higher flexibility compared to hardware redundancy, as a broad variety of virtual components can be spawned, adapted and replaced in a short time. Also, as no additional hardware is necessary, the incurred costs decrease significantly. In addition to that, most of the virtualized components are deployed on Commercial-Off-The-Shelf (COTS) hardware solutions, further increasing the monetary benefit. The approach is developed by first reviewing currently suggested solutions for AMIs and related services. Using this information, virtualization technologies are investigated for their performance influences, before a virtualized service infrastructure is devised, which replaces selected components by virtualized counterparts. Next, a novel model, which allows the separation of services and hosting substrates is developed, allowing the introduction of virtualization technologies to abstract from the underlying architecture. Third, the performability as well as monetary savings are investigated by evaluating the developed approach in several scenarios using analytical and simulative model analysis as well as proof-of-concept approaches. Last, the practical applicability and possible regulatory challenges of the approach are identified and discussed. Results confirm that—under certain assumptions—the developed virtualized AMI is superior to the currently suggested architecture. The availability of services can be severely increased and network delays can be minimized through centralized hosting. The availability can be increased from 96.82% to 98.66% in the given scenarios, while decreasing the costs by over 60% in comparison to the currently suggested AMI architecture. Lastly, the performability analysis of a virtualized service prototype employing performance analysis and a Musa-Okumoto approach reveals that the AMI requirements are fulfilled. KW - Advanced Metering Infrastructure KW - Virtualization KW - Performability KW - Energieversorgung KW - Virtualisierung Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8597 ER - TY - THES A1 - Hatzesberger, Simon T1 - Strongly Asymptotically Optimal Methods for the Pathwise Global Approximation of Stochastic Differential Equations with Coefficients of Super-linear Growth N2 - Our subject of study is strong approximation of stochastic differential equations (SDEs) with respect to the supremum and the L_p error criteria, and we seek approximations that are strongly asymptotically optimal in specific classes of approximations. For the supremum error, we prove strong asymptotic optimality for specific tamed Euler schemes relating to certain adaptive and to equidistant time discretizations. For the L_p error, we prove strong asymptotic optimality for specific tamed Milstein schemes relating to certain adaptive and to equidistant time discretizations. To illustrate our findings, we numerically analyze the SDE associated with the Heston–3/2–model originating from mathematical finance. KW - Stochastic differential equation KW - Strong approximation KW - Strong asymptotic optimality KW - Asymptotic lower error bounds KW - Asymptotic upper error bounds KW - Stochastische Differentialgleichung KW - Approximation Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-8100 ER - TY - THES A1 - Alhamzeh, Alaa T1 - Language Reasoning by means of Argument Mining and Argument Quality N2 - Understanding of financial data has always been a point of interest for market participants to make better informed decisions. Recently, different cutting edge technologies have been addressed in the Financial Technology (FinTech) domain, including numeracy understanding, opinion mining and financial ocument processing. In this thesis, we are interested in analyzing the arguments of financial experts with the goal of supporting investment decisions. Although various business studies confirm the crucial role of argumentation in financial communications, no work has addressed this problem as a computational argumentation task. In other words, the automatic analysis of arguments. In this regard, this thesis presents contributions in the three essential axes of theory, data, and evaluation to fill the gap between argument mining and financial text. First, we propose a method for determining the structure of the arguments stated by company representatives during the public announcement of their quarterly results and future estimations through earnings conference calls. The proposed scheme is derived from argumentation theory at the micro-structure level of discourse. We further conducted the corresponding annotation study and published the first financial dataset annotated with arguments: FinArg. Moreover, we investigate the question of evaluating the quality of arguments in this financial genre of text. To tackle this challenge, we suggest using two levels of quality metrics, considering both the Natural Language Processing (NLP) literature of argument quality assessment and the financial era peculiarities. Hence, we have also enriched the FinArg data with our quality dimensions to produce the FinArgQuality dataset. In terms of evaluation, we validate the principle of ensemble learning on the argument identification and argument unit classification tasks. We show that combining a traditional machine learning model along with a deep learning one, via an integration model (stacking), improves the overall performance, especially in small dataset settings. In addition, despite the fact that argument mining is mainly a domain dependent task, to this date, the number of studies that tackle the generalization of argument mining models is still relatively small. Therefore, using our stacking approach and in comparison to the transfer learning model of DistilBert, we address and analyze three real-world scenarios concerning the model robustness over completely unseen domains and unseen topics. Furthermore, with the aim of the automatic assessment of argument strength, we have investigated and compared different (refined) versions of Bert-based models that incorporate external knowledge in the decision layer. Consequently, our method outperforms the baseline model by 13 ± 2% in terms of F1-score through integrating Bert with encoded categorical features. Beyond our theoretical and methodological proposals, our model of argument quality assessment, annotated corpora, and evaluation approaches are publicly available, and can serve as strong baselines for future work in both FinNLP and computational argumentation domains. Hence, directly exploiting this thesis, we proposed to the community, a new task/challenge related to the analysis of financial arguments: FinArg-1, within the framework of the NTCIR-17 conference. We also used our proposals to react to the Touché challenge at the CLEF 2021 conference. Our contribution was selected among the «Best of Labs». KW - NLP, Argument Mining, Argument Quality Assessment, Financial Argumentation, Earnings Conference Calls Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-12699 ER - TY - THES A1 - Klaghstan, Merza T1 - Multimedia data dissemination in opportunistic systems N2 - Opportunistic networks (OppNets) are human-centric mobile ad-hoc networks, in which neither the topology nor the participating nodes are known in advance. Routing is dynamically planned following the store-carry-and-forward paradigm, which takes advantage of people mobility. This widens the range of communication and supports indirect end-to-end data delivery. But due to individuals’ mobility, OppNets are characterized by frequent communication disruptions and uncertain data delivery. Hence, these networks are mostly used for exchanging small messages like disaster alarms or traffic notifications. Other scenarios that require the exchange of larger data (e.g. video) are still challenging due to the characteristics of this kind of networks. However, there are still multimedia sharing scenarios where a user might need switching from infrastructural communications to an ad-hoc alternative. Examples are the cases of 1) absence of infrastructural networks in far rural areas, 2) high costs due to roaming or limited data volumes or 3) undesirable censorship by third parties while exchanging sensitive content. Consequently, we target in this thesis a video dissemination scheme in OppNets. For the video delivery problem in the sparse opportunistic networks, we propose a solution with the objective of reducing the video playout delay, so that enabling the recipient to play the video content as soon as possible even if at a low quality. Furthermore, the received video reaches later a higher quality level, ensuring a better viewing experience. The proposed solution encloses three contributions. The first one is given by granulating the videos at the source node into smaller parts, and associating them with unequal redundancy degrees. This is technically based on using the Scalable Video Coding (SVC), which encodes a video into several layers of unequal importance for viewing the content at different quality levels. Layers are routed using the Spray-and-Wait routing protocol, with different redundancy factors for the different layers depending on their importance degree. In this context as well, a video viewing QoE metric is proposed, which takes the values of the perceived video quality, delivery delay and network overhead into consideration, and on a scalable basis. Second, we take advantage of the small units of the Network Abstraction Layer (NAL), which compose SVC layers. NAL units are packetized together under specific size constraints to optimize granularity. Packets sizes are tuned in an adaptive way, with regard to the dynamic network conditions. Each node is enabled to record a history of environmental information regarding the contacts and forwarding opportunities, and use this history to predict future opportunities and optimize the sizes accordingly. Lastly, the receiver (destination) node is pushed into action by reacting to missing data parts in a composite ``backward'' loss concealment mechanism. So, the receiver asks first for the missing data from other nodes in the network in the form of request-response. Then, since the transmission is concerned with video content, video frame loss error concealment techniques are also exploited at the receiver side. Consequently, we propose to combine the two techniques in the loss concealment mechanism, which is enabled then to react to missing data parts. To study the feasibility and the applicability of the proposed solutions, simulation-driven experiments are performed, and statistical results are collected and analyzed. Consequently, we have got promising results that show the applicability of video dissemination in opportunistic delay tolerant networks, and open the door for a range of possible future works. KW - Opportunistisches Netzwerk KW - Multimedia KW - Videoübertragung Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4438 ER - TY - THES A1 - He, Xiaobing T1 - Threat Assessment for Multistage Cyber Attacks in Smart Grid Communication Networks N2 - In smart grids, managing and controlling power operations are supported by information and communication technology (ICT) and supervisory control and data acquisition (SCADA) systems. The increasing adoption of new ICT assets in smart grids is making smart grids vulnerable to cyber threats, as well as raising numerous concerns about the adequacy of current security approaches. As a single act of penetration is often not sufficient for an attacker to achieve his/her goal, multistage cyber attacks may occur. Due to the interdependence between the power grid and the communication network, a multistage cyber attack not only affects the cyber system but impacts the physical system. This thesis investigates an application-oriented stochastic game-theoretic cyber threat assessment framework, which is strongly related to the information security risk management process as standardized in ISO/IEC 27005. The proposed cyber threat assessment framework seeks to address the specific challenges (e.g., dynamic changing attack scenarios and understanding cascading effects) when performing threat assessments for multistage cyber attacks in smart grid communication networks. The thesis looks at the stochastic and dynamic nature of multistage cyber attacks in smart grid use cases and develops a stochastic game-theoretic model to capture the interactions of the attacker and the defender in multistage attack scenarios. To provide a flexible and practical payoff formulation for the designed stochastic game-theoretic model, this thesis presents a mathematical analysis of cascading failure propagation (including both interdependency cascading failure propagation and node overloading cascading failure propagation) in smart grids. In addition, the thesis quantifies the characterizations of disruptive effects of cyber attacks on physical power grids. Furthermore, this thesis discusses, in detail, the ingredients of the developed stochastic game-theoretic model and presents the implementation steps of the investigated stochastic game-theoretic cyber threat assessment framework. An application of the proposed cyber threat assessment framework for evaluating a demonstrated multistage cyber attack scenario in smart grids is shown. The cyber threat assessment framework can be integrated into an existing risk management process, such as ISO 27000, or applied as a standalone threat assessment process in smart grid use cases. KW - Smart Grids KW - Game Theory KW - Cascading Failures KW - Threat Assessment KW - Communication Networks KW - Intelligentes Stromnetz KW - Sicherheit KW - Spieltheorie Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5051 ER - TY - THES A1 - Niklaus, Christina T1 - From Complex Sentences to a Formal Semantic Representation using Syntactic Text Simplification and Open Information Extraction N2 - Sentences that present a complex linguistic structure act as a major stumbling block for Natural Language Processing (NLP) applications whose predictive quality deteriorates with sentence length and complexity. The task of Text Simplification (TS) may remedy this situation. It aims to modify sentences in order to make them easier to process, using a set of rewriting operations, such as reordering, deletion or splitting. These transformations are executed with the objective of converting the input into a simplified output, while preserving its main idea and keeping it grammatically sound. State-of-the-art syntactic TS approaches suffer from two major drawbacks: first, they follow a very conservative approach in that they tend to retain the input rather than transforming it, and second, they ignore the cohesive nature of texts, where context spread across clauses or sentences is needed to infer the true meaning of a statement. To address these problems, we present a discourse-aware TS framework that is able to split and rephrase complex English sentences within the semantic context in which they occur. By generating a fine-grained output with a simple canonical structure that is easy to analyze by downstream applications, we tackle the first issue. For this purpose, we decompose a source sentence into smaller units by using a linguistically grounded transformation stage. The result is a set of selfcontained propositions, with each of them presenting a minimal semantic unit. To address the second concern, we suggest not only to split the input into isolated sentences, but to also incorporate the semantic context in the form of hierarchical structures and semantic relationships between the split propositions. In that way, we generate a semantic hierarchy of minimal propositions that benefits downstream Open Information Extraction (IE) tasks. To function well, the TS approach that we propose requires syntactically well-formed input sentences. It targets generalpurpose texts in English, such as newswire or Wikipedia articles, which commonly contain a high proportion of complex assertions. In a second step, we present a method that allows state-of-the-art Open IE systems to leverage the semantic hierarchy of simplified sentences created by our discourseaware TS approach in constructing a lightweight semantic representation of complex assertions in the form of semantically typed predicate-argument structures. In that way, important contextual information of the extracted relations is preserved that allows for a proper interpretation of the output. Thus, we address the problem of extracting incomplete, uninformative or incoherent relational tuples that is commonly to be observed in existing Open IE approaches. Moreover, assuming that shorter sentences with a more regular structure are easier to process, the extraction of relational tuples is facilitated, leading to a higher coverage and accuracy of the extracted relations when operating on the simplified sentences. Aside from taking advantage of the semantic hierarchy of minimal propositions in existing Open IE Abstract approaches, we also develop an Open IE reference system, Graphene. It implements a relation extraction pattern upon the simplified sentences. The framework we propose is evaluated within our reference TS implementation DisSim. In a comparative analysis, we demonstrate that our approach outperforms the state of the art in structural TS both in an automatic and a manual analysis. It obtains the highest score on three simplification datasets from two different domains with regard to SAMSA (0.67, 0.57, 0.54), a recently proposed metric targeted at automatically measuring the syntactic complexity of sentences which highly correlates with human judgments on structural simplicity and grammaticality. These findings are supported by the ratings from the human evaluation, which indicate that our baseline implementation DisSim returns fine-grained simplified sentences that achieve a high level of syntactic correctness and largely preserve the meaning of the input. Furthermore, a comparative analysis with the annotations contained in the RST Discourse Treebank (RST-DT) reveals that we are able to capture the contextual hierarchy between the split sentences with a precision of approximately 90% and reach an average precision of almost 70% for the classification of the rhetorical relations that hold between them. Finally, an extrinsic evaluation shows that when applying our TS framework as a pre-processing step, the performance of state-ofthe-art Open IE systems can be improved by up to 32% in precision and 30% in recall of the extracted relational tuples. Accordingly, we can conclude that our proposed discourse-aware TS approach succeeds in transforming sentences that present a complex linguistic structure into a sequence of simplified sentences that are to a large extent grammatically correct, represent atomic semantic units and preserve the meaning of the input. Moreover, the evaluation provides sufficient evidence that our framework is able to establish a semantic hierarchy between the split sentences, generating a fine-grained representation of complex assertions in the form of hierarchically ordered and semantically interconnected propositions. Finally, we demonstrate that state-of-the-art Open IE systems benefit from using our TS approach as a pre-processing step by increasing both the accuracy and coverage of the extracted relational tuples for the majority of the Open IE approaches under consideration. In addition, we outline that the semantic hierarchy of simplified sentences can be leveraged to enrich the output of existing Open IE systems with additional meta information, thus transforming the shallow semantic representation of state-of-the-art approaches into a canonical context-preserving representation of relational tuples. KW - Text Simplification KW - Syntactic Simplification KW - Open Information Extraction KW - Semantic Representation KW - Complex Sentences Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-10540 ER - TY - THES A1 - Mandarawi, Waseem T1 - Multi-objective Network Virtualization and its Applicability to Industrial Networks N2 - Network virtualization provides high flexibility for deploying communication services in dense and heterogeneous environments. Two main approaches (dimensions) that are usually combined exist: Network Function Virtualization (NFV) technologies for functionality virtualization and Virtual Network Embedding (VNE) algorithms for resource virtualization. These approaches can be applied to different network levels, such as factory and enterprise levels of industrial networks. Several objectives and constraints, that might be conflicting, shall be considered when network virtualization is applied, mainly in complex topologies. This thesis proposes a network virtualization model that considers both virtualization dimensions, two network levels, and different objectives and constraints. The network levels considered are two primary levels in industrial networks. However, this consideration does not restrict the model to a particular environment or certain levels. The considered objectivities/constraints are topology, reliability, security, performance, and resource usage. Based on this model, we first build an overall combined solution for autonomic and composite virtual networking. This solution considers both virtualization dimensions, two network levels, and target objectives. Furthermore, this solution combines three novel virtualization sub-approaches that consider performance, reliability, and performance. However, the sub-approaches apply to different combinations of levels and dimensions, and the reliability approach additionally considers the resource usage objective. After presenting all solutions, we map them to the defined model. Regarding applicability to industrial networks, the combined approach is applied to an enterprise-level Industrial Internet of Things (IIoT) use case inspired by the smart factory concept in Industry 4.0. However, the sub-approaches are applied to more specific use cases. The performance and reliability solutions are integrated with relevant components of the Time Sensitive Networks (TSN) standard as a modern technology for industrial networks. The goal is to enrich the reliability and performance capabilities of TSN with the flexibility of network virtualization. In the combined approach, we compose and embed an environment-aware Extended Virtual Network (EVN) that represents the physical devices, virtual application functions, and required Service Function Chains (SFCs). We use the graph transformation method to transform abstract application requirements (represented by an Application Request (AR)) into an EVN. Both EVN composition and embedding methods consider the Substrate Network (SN) topology and different security, reliability, performance, and resource usage policies. These policies are applied with a certain priority and depend on the properties of communicating entities such as location and type. The EVN is embedded using property-based node mapping, reliability-aware branching, and a greedy chain embedding heuristic. The chain embedding heuristic is evaluated using a random topology that represents the use case. The performance sub-approach is NFV-based and is applied to a specific use case with Time-critical Traffic (TCT) flows. We develop and evaluate a complete framework for virtualizing Time-aware Shaper (TAS) using high-performance NFV. The reliability sub-approach is VNE-based and is applied to a specific factory level use case. We develop minimal and maximal branching heuristics based on a reliability-aware k-shortest path algorithm and compare them using a typical factory topology. We then integrate these algorithms with a Frame Replication and Elimination for Reliability (FRER) simulator to realize reliability policies by the autonomic and efficient configuration of a supporting technology. The security sub-approaches are related to both virtualization dimensions and are applied to generic enterprise-level use cases. However, the applicability of the security aspect to industrial networks is only shown in the combined (EVN) approach and its use case. We research the autonomic security management in Network Function Virtualization Infrastructure (NFVI) with the main goal of early reaction to threats through SFC reconfiguration through Virtual Network Function (VNF) live migration. This goal is approached by supporting the security measurements with a decision making architecture that considers, on the one hand, the threats and events in the environment and, on the other hand, the Service Level Agreement (SLA) between the NFVI provider and user. For this purpose, we classify the VNF-specific attacks and define possible early detectable behavior patterns. Finally, we develop a security-aware VNE heuristic that considers the security requirements of the Virtual Network (VN) and the security capabilities of the SN. This approach is modified in the combined approach to consider deploying virtualized security VNFs. KW - Network Virtualization KW - Industrial Networks KW - Virtual Network Embedding KW - Network Function Virtualization KW - Time Sensitive Networking Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-10606 ER - TY - THES A1 - Alyousef, Ammar T1 - E-Mobility Management: Towards a Grid-friendly Smart Charging Solution N2 - Replacing fossil-fueled vehicles with Electric Vehicles (EVs) poses new challenges for power distribution networks. Specifically speaking, the electrification of the mobility sector relies on the ability to process and analyze information on when, where, for how long, or how fast charging processes will take place. Nevertheless, such kind of information is typically difficult to acquire or insufficiently predictable due to the dynamic nature of the system. Also, the increasing adoption rate of the renewable energy sources, specifically the domestic Photovoltaic (PV) systems, and the potentially associated grid defection scenarios will significantly impact the cost and efforts required to operate the grid in terms of power quality and demand-supply aspects. However, such emerging requirements have arguably not been taken into account when the distribution grid was built originally. Besides, expanding the distribution and transmission capacity is a very costly and lengthy process. Therefore, any proposed solution should be cost-effective as well as environment-, grid- and user-friendly. To this end, the advancements in Information and Communications Technology (ICT) are increasingly adopted and applied. This thesis addresses the rapidly growing EV sector and deals with the problems to overcome potential power quality degradation caused by the challenges mentioned above. Since time switch and radio ripple control as existing solutions in Germany are costly and neither very effective nor scalable as it requires hardware retrofitting of existing public Charging Stations (CSs), the primary focus of this work is the development of an appropriate, standards-based, scalable, and smart charging solution of EVs. Such a solution can, in turn, boost the usage of renewable energy by ensuring that the existing grid infrastructure can operate within its permissible limits while maintaining acceptable levels of power quality. This work introduces a new definition of the concept, “grid-friendly EV charging”, where the power demand of a CS is adjusted depending on the real-time status of a power grid. In this regard, the conflicting concerns of stakeholders in an EV ecosystem are considered. For example, a Distribution System Operator (DSO) does not want to reveal a lot of technical details about the power grid or its status. Similarly, a Charging Service Provider (CSP) wants to keep its clients happy without sharing the details of its business model with others, namely, DSOs. For that sake, a distributed smart charging architecture is proposed in this thesis. It is event-driven and responds in nearly real-time to unforeseen and critical grid situations such as high/low voltage, congestion, phase unbalance, and harmonics. In that regard, the publish/subscribe messaging pattern, used as a part of the architecture, enables an efficient and well-performing communication scheme among the different components. Moreover, an indication mechanism about the different issues in a power grid is developed; it adopts the traffic light model. It works as a black box to separate smart controllers for each CS and configured only by the CSP. Smart chargers enable a smooth adjustment of the charging power to avoid drastic changes in the grid state. To that end, two types of intelligent controllers are developed and tested. While the first controller is inspired by the fuzzy logic, the second one is inspired by the slow-start mechanism used in TCP to control congestion in computer networks. A simulative approach is applied to evaluate the solution, thereby, a topology of a real low voltage grid with realistic load and generation profiles is used. Furthermore, a set of metrics is defined regarding the main concerns of stakeholders: voltage, overloading, fairness, the satisfaction of EV users and grid operator, as well as the grid-friendly behavior of a CS/ EV user. The evaluation shows that the solution is able to guarantee a safe operation of the grid. The proposed system can ensure a grid-friendly charging by sacrificing of a small portion of user satisfaction, that sacrifice of a user is awarded via a points-based reward system. Last but not least, the proposed distributed controllers are compared to two other controllers: (1) a decentralized controller based only on sensing the local voltage and (2) a very strict centralized controller focusing on grid-friendliness. The latter ensures proportional fairness among users regarding the objective function of the optimization problem solved in each simulation step. The distributed controllers are superior to the decentralized controller in terms of grid friendly and fairness and converge in general to the centralized one. KW - E-Mobility KW - Smart Charging KW - Grid-Friendliness KW - Elektromobilität KW - Lademanagement KW - Netzstabilität Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-9302 ER - TY - THES A1 - Schmid, Matthias T1 - Towards Storing 3D Model Graphs in Relational Databases N2 - The increasing relevance of massive graph data reinforces the need for adequate graph data management. While several graph database engines have been developed, the storage of graph data in a relational database management system, and therefore the seamless integration into existing information systems remains an open challenge. Motivated by the use case to integrate Building Information Modeling (BIM) data into the MonArch system, we propose a solution that transforms the BIM data into a property graph and stores this graph in the database system. We present a novel approach to efficiently store property graph data in a relational database management system using JSON functionality and redundant storage of edges in adjacency lists and show how to import huge data sets into this schema. Applying this approach, we import data sets of up to nearly 1 TB of disk space within the relational database, while only having 96 GB of main memory available. We also present a new approach of how to retrieve data from this database schema, translating queries written in the popular property graph query language Cypher into SQL. Hence, we provide an intuitive way to write semantically complex queries. We also demonstrate the efficiency of our approach using the standardized Linked Data Benchmark Council – Social Network Benchmark (LDBC - SNB) framework. Our approach increases the throughput for this benchmark by up to 85 times, compared to existing approaches for RDBMS. In addition, we propose a new method to transform BIM data into the property graph model and how to apply the aforementioned property graph storage to this data. We can import IFC models of up to 300 MB within five minutes. We show the suitability of our approach using our own use case specific benchmark, which we integrated into the previously mentioned Social Network Benchmark. For our interactive use case-specific queries, we achieve response times faster than 5 ms in 99% of all executions. Finally, we present how the aforementioned approach to store BIM data in a relational database management system is integrated into the existing MonArch system by splitting the different functionalities of our approach into a microservice architecture. N2 - Die steigende Relevanz von riesigen Graphdatenmengen verstärkt die Notwendigkeit von adäquatem Graphdaten Management. Während bereits mehrere Graphdatenbanken entwickelt wurden, bleibt die Speicherung von Graphdaten in relationalen Datenbanken und die damit verbundene nahtlose Integration in bereits existierende Informationssysteme eine ungelöste Herausforderung. Motiviert durch unseren eigenen Anwendungsfall Building Information Modeling (BIM)Daten in das MonArch Informationssystem zu integrieren, schlagen wir einen Ansatz vor, BIM Daten in eine Property Graph Form umzuwandeln und diesen in der Datenbank zu speichern. Um dies zu erreichen, stellen wir einen neuartigen Ansatz vor, um Property Graphen in einem relationalen Datenbanksystem zu speichern, indem wir Funktionalitäten wie JSON und die redundante Speicherung von Kanten in Adjazenzlisten kombinieren und zeigen wie große Mengen dieser Daten in das Schema importiert werden können. Durch die Anwendung unseres Ansatzes können wir Datensätze von bis zu 1 TB in das Datenbanksystem importieren, während wir nur 96 GB Hauptspeicher zur Verfügung haben. Wir stellen außerdem einen neuen Ansatz vor, um Daten aus dem zuvor genannten Schema abzufragen, indem wir die beliebte Graphanfragesprache Cypher in die Sprache SQL übersetzen. Dadurch erreichen wir eine intuitive Art semantisch komplexe Anfragen zu schreiben. Zusätzlich zeigen wir die Effizienz unseres Ansatzes, indem wir das standardisierte Evaluationsframework Social Network Benchmark des Linked Data Benchmar Council (LDBC – SNB) verwenden. Unser Ansatz erhöht den Durchsatz dieses Benchmarks, im Vergleich zu existierenden Ansätzen für relationale Datenbanksysteme, auf einen bis zu 85-fachen Durchsatz. Zusätzlich schlagen wir eine neue Methode vor, um BIM Daten in das Property Graph Modell zu übertragen und wie das zuvor vorgestellte Speichermodel verwendet werden kann, um diese Daten zu speichern. Damit können wir IFC Modelle mit bis zu 300 MB in unter 5 Minuten in unser System importieren. Schließlich zeigen wir die Eignung unseres Ansatzes, indem wir einen eigenen Benchmark spezifisch für unseren Anwendungsfall verwenden, welchen wir in den zuvor erwähnte Social Network Benchmark integriert haben. Für unsere anwendungsfallspezifischen Anfragen erreichen wir Antwortzeiten von unter 5 ms in 99% der Ausführungen. KW - Graph-based database models KW - Relational database model KW - Property graph KW - Industry Foundation Classes KW - IFC Store Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-10353 ER - TY - THES A1 - Schlenker, Florian T1 - Delaunay Configuration B-Splines N2 - The generalization of univariate splines to higher dimensions is not straightforward. There are different approaches, each with its own advantages and drawbacks. A promising approach using Delaunay configurations and simplex splines is due to Neamtu. After recalling fundamentals of univariate splines, simplex splines, and the wellknown, multivariate DMS-splines, we address Neamtu’s DCB-splines. He defined two variants that we refer to as the nonpooled and the pooled approach, respectively. Regarding these spline spaces, we contribute the following results. We prove that, under suitable assumptions on the knot set, both variants exhibit the local finiteness property, i.e., these spline spaces are locally finite-dimensional and at each point only a finite number of basis candidate functions have a nonzero value. Additionally, we establish a criterion guaranteeing these properties within a compact region under mitigated assumptions. Moreover, we show that the knot insertion process known from univariate splines does not work for DCB-splines and reason why this behavior is inherent to these spline spaces. Furthermore, we provide a necessary criterion for the knot insertion property to hold true for a specific inserted knot. This criterion is also sufficient for bivariate, nonpooled DCB-splines of degrees zero and one. Numerical experiments suggest that the sufficiency also holds true for arbitrary spline degrees. Univariate functions can be approximated in terms of splines using the Schoenberg operator, where the approximation error decreases quadratically as the maximum distance between consecutive knots is reduced. We show that the Schoenberg operator can be defined analogously for both variants of DCB-splines with a similar error bound. Additionally, we provide a counterexample showing that the basis candidate functions of nonpooled DCB-splines are not necessarily linearly independent, contrary to earlier statements in the literature. In particular, this implies that the corresponding functions are not a basis for the space of nonpooled DCB-splines. N2 - Univariate Splines können nicht unmittelbar auf mehrere Dimensionen verallgemeinert werden. Jedoch gibt es verschiedene Ansätze mit jeweils unterschiedlichen Vor- und Nachteilen. Eine vielversprechende Herangehensweise, die Delaunay-Konfigurationen und Simplex-Splines verwendet, stammt von Neamtu. Nachdem wir die Grundlagen von univariaten Splines, Simplex-Splines und den bekannten multivariaten DMS-Splines wiederholt haben, beschäftigen wir uns mit Neamtus DCB-Splines. Er führte zwei verschiedene Varianten ein, die als nichtaggregierter beziehungsweise aggregierter Ansatz bezeichnet werden. In Bezug auf diese Splineräume präsentieren wir die folgenden Ergebnisse. Wir zeigen zum einen, dass beide Varianten unter geeigneten Voraussetzungen an die Knotenmenge die sogenannte Lokale-Endlichkeits-Eigenschaft besitzen. Dies bedeutet, dass die Splineräume lokal endlichdimensional sind und dass an jedem Punkt nur eine endliche Anzahl der Kandidaten an Basisfunktionen einen von null verschiedenen Wert aufweist. Zusätzlich ermitteln wir ein Kriterium, welches diese Eigenschaften auf einem kompakten Gebiet auch unter schwächeren Voraussetzungen garantiert. Darüber hinaus zeigen wir, dass der von den univariaten Splines her bekannte Prozess des Knoteneinfügens für DCB-Splines nicht funktioniert, und begründen, warum dieses Verhalten in der Natur dieser Splineräume liegt. Außerdem geben wir ein notwendiges Kriterium dafür an, dass die Knoteneinfüge-Eigenschaft für einen bestimmten einzufügenden Knoten gegeben sein kann. Für bivariate nicht-aggregierte DCB-Splines von Grad null und eins ist dieses Kriterium auch hinreichend. Numerische Experimente legen ferner die Vermutung nahe, dass dies unabhängig vom Splinegrad der Fall ist. Univariate Funktionen können mithilfe des Schoenberg-Operators durch Splines approximiert werden. Dabei hat eine Verringerung des maximalen Abstands zweier aufeinanderfolgender Knoten eine quadratische Verringerung des Approximationsfehlers zur Folge. Wir zeigen, dass der Schoenberg-Operator für beide Variaten von DCB-Splines auf analoge Art und Weise und mit einer ähnlichen Fehlerschranke definiert werden kann. Zusätzlich geben wir ein Gegenbeispiel an, das zeigt, dass die Basisfunktions-Kandidaten der nicht-aggregierten DCB-Splines nicht notwendigerweise linear unabhängig sind, was einen Gegensatz zu früheren Behauptungen in der Literatur darstellt. Dies impliziert insbesondere, dass die entsprechenden Funktionen keine Basis für den Raum der nicht-aggregierten DCB-Splines bilden. KW - Multivariate splines KW - Simplex splines KW - Delaunay triangulations KW - Delaunay configurations KW - Neamtu, Marian KW - Spline KW - Bivariater Spline KW - Spline-Raum KW - Simplexspline KW - Neamtu, Marian Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-11225 ER - TY - THES A1 - Sonnleitner, Mathias T1 - The power of random information for numerical approximation and integration N2 - This thesis investigates the quality of randomly collected data by employing a framework built on information-based complexity, a field related to the numerical analysis of abstract problems. The quality or power of gathered information is measured by its radius which is the uniform error obtainable by the best possible algorithm using it. The main aim is to present progress towards understanding the power of random information for approximation and integration problems. In the first problem considered, information given by linear functionals is used to recover vectors, in particular from generalized ellipsoids. This is related to the approximation of diagonal operators which are important objects of study in the theory of function spaces. We obtain upper bounds on the radius of random information both in a convex and a quasi-normed setting, which extend and, in some cases, improve existing results. We conjecture and partially establish that the power of random information is subject to a dichotomy determined by the decay of the length of the semiaxes of the generalized ellipsoid. Second, we study multivariate approximation and integration using information given by function values at sampling point sets. We obtain an asymptotic characterization of the radius of information in terms of a geometric measure of equidistribution, the distortion, which is well known in the theory of quantization of measures. This holds for isotropic Sobolev as well as Hölder and Triebel-Lizorkin spaces on bounded convex domains. We obtain that for these spaces, depending on the parameters involved, typical point sets are either asymptotically optimal or worse by a logarithmic factor, again extending and improving existing results. Further, we study isotropic discrepancy which is related to numerical integration using linear algorithms with equal weights. In particular, we analyze the quality of lattice point sets with respect to this criterion and obtain that they are suboptimal compared to uniform random points. This is in contrast to the approximation of Sobolev functions and resolves an open question raised in the context of a possible low discrepancy construction on the two-dimensional sphere. KW - information-based complexity KW - cubature KW - numerical approximation KW - discrepancy KW - Monte Carlo integration KW - Komplexität / Algorithmus KW - Numerische Integration KW - Monte-Carlo-Integration KW - Gewichteter Funktionenraum KW - Scattered-Data-Interpolation Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-11305 ER - TY - THES A1 - Silva, Vivian dos Santos T1 - A Composite Syntactic-Semantic Interpretable Text Entailment Approach Exploring Commonsense Knowledge Graphs N2 - Natural Language Processing has an important role in Artificial Intelligence for easing human-machine interaction. Processing human language, though, poses many challenges, among which is the semantics-related phenomenon known as language variability, the fact that the same thing can be said in several ways. NLP applications' inputs and outputs can be expressed in different forms, whose equivalence can be verified through inference. The textual entailment paradigm was established to enable the creation of a unifying framework for applied inference, providing a means of delivering other NLP task from handling inference issues in an ad-hoc manner, using instead the outputs of an inference-dedicated mechanism. Text entailment, the task of determining whether a piece of text logically follows from another piece of text, involves different scenarios, which can range from a simple syntactic variation to more complex semantic relationships between sentences. However, most approaches try a one-size-fits-all solution that usually favors some scenario to the detriment of another. The commonsense world knowledge necessary to support more complex inferences is also usually employed in a limited way, with most approaches sticking to shallow semantic information, leaving more elaborate semantic relationships aside. Furthermore, most systems still work as a "black box", providing a yes/no answer that does not explain the underlying reasoning process. This thesis aims at addressing these issues by proposing a composite interpretable approach for recognizing text entailment where the entailment pair is analyzed so the most relevant phenomenon is detected and the suitable method can be used to solve it. Syntactic variations are dealt with through the analysis of the sentences' syntactic structures, and semantic relationships are detected with the aid of a knowledge graph built from natural language dictionary definitions. Also, if a semantic matching is involved, the answer is made interpretable through the generation of natural language justifications that explain the semantic relationship between the pieces of text. The result is the XTE - Explainable Text Entailment - a system that outperforms well-established tools based on single-technique entailment algorithms, and that also gives an important step towards Explainable AI, allowing the inference model interpretation, making the semantic reasoning process explicit and understandable. KW - Textual Entailment KW - Knowledge Graph KW - Semantic Interpretability Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-10706 ER - TY - THES A1 - Schmid, Josef T1 - Learning-Based Quality of Service Prediction in Cellular Vehicle Communication N2 - Network communication has become a part of everyday life, and the interconnection among devices and people will increase even more in the future. A new area where this development is on the rise is the field of connected vehicles. It is especially useful for automated vehicles in order to connect the vehicles with other road users or cloud services. In particular for the latter it is beneficial to establish a mobile network connection, as it is already widely used and no additional infrastructure is needed. With the use of network communication, certain requirements come along. One of them is the reliability of the connection. Certain Quality of Service (QoS) parameters need to be met. In case of degraded QoS, according to the SAE level specification, a downgrade of the automated system can be required, which may lead to a takeover maneuver, in which control is returned back to the driver. Since such a handover takes time, prediction is necessary to forecast the network quality for the next few seconds. Prediction of QoS parameters, especially in terms of Throughput (TP) and Latency (LA), is still a challenging task, as the wireless transmission properties of a moving mobile network connection are undergoing fluctuation. In this thesis, a new approach for prediction Network Quality Parameters (NQPs) on Transmission Control Protocol (TCP) level is presented. It combines the knowledge of the environment with the low level parameters of the mobile network. The aim of this work is to perform a comprehensive study of various models including both Location Smoothing (LS) grid maps and Learning Based (LB) regression ones. Moreover, the possibility of using the location independence of a model as well as suitability for automated driving is evaluated. N2 - Netzwerkkommunikation ist zu einem Teil des täglichen Lebens geworden, und die Vernetzung von Geräten und Menschen wird in Zukunft noch weiter zunehmen. Ein neuer Bereich, in dem diese Entwicklung zunimmt, sind vernetzte Fahrzeuge. Es ist vorteilhaft automatisierte Fahrzeuge mit anderen Verkehrsteilnehmern oder Cloud-Diensten zu verbinden. Insbesondere für letztere ist der Einsatz einer mobilen Netzwerkverbindung zweckmäßig, da sie bereits weit verbreitet ist und keine zusätzliche Infrastruktur erfordert. Mit der Nutzung des Netzwerkes gehen auch einige Anforderungen einher. Die Zuverlässigkeit der Verbindung ist entscheidend. Kann keine ausreichende Qualität der Verbindung erfüllt werden kann nach SAE Spezifikation das Herunterstufen der Automatisierungsstufe erforderlich sein. In letzter Konsequenz kann diese schließlich zu einem Übernahmemanöver führen, wobei die Kontrolle wieder an den Fahrer zurückgegeben wird. Da ein solcher Wechsel Zeit in Anspruch nimmt, ist eine Vorhersage erforderlich, um die Netzqualität in den nächsten Sekunden zu prognostizieren. Eine solche Vorhersage der Dienstgüte (Quality of Service (QoS)), besonders hinsichtlich Durchsatz und Latenz, nach wie vor eine recht anspruchsvolle Aufgabe, da die drahtlosen Übertragungseigenschaften einer sich bewegenden mobilen Netzwerkverbindung großen Schwankungen unterliegen. In dieser Dissertation wird ein neuer Ansatz für die Vorhersage von Network Quality Parameters (NQPs) auf der Ebene des Transmission Control Protocol (TCP) vorgestellt. Er kombiniert das Wissen der Umgebung mit den Parametern des Mobilfunknetzes. Das Ziel dieser Arbeit ist eine umfangreiche Untersuchung verschiedener Modelle, darunter sind sowohl Lokalisationsglättende Kachel-Karten wie auch Regressionsverfahren aus dem Bereich des Maschinellen Lernens. Darüber hinaus wird dessen die Möglichkeit der Nutzung der Ortsunabhängigkeit eines Modells erörtert sowie Eignung für automatisiertes Fahren evaluiert. Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-10772 ER - TY - THES A1 - Mexis, Nico T1 - A Comprehensive Comparison of Fuzzy Extractor Schemes Employing Different Error Correction Codes N2 - This thesis deals with fuzzy extractors, security primitives often used in conjunction with Physical Unclonable Functions (PUFs). A fuzzy extractor works in two stages: The generation phase and the reproduction phase. In the generation phase, an Error Correction Code (ECC) is used to compute redundant bits for a given PUF response, which are then stored as helper data, and a key is extracted from the response. Then, in the reproduction phase, another (possibly noisy) PUF response can be used in conjunction with this helper data to extract the original key. It is clear that the performance of the fuzzy extractor is strongly dependent on the underlying ECC. Therefore, a comparison of ECCs in the context of fuzzy extractors is essential in order to make them as suitable as possible for a given situation. It is important to note that due to the plethora of various PUFs with different characteristics, it is very unrealistic to propose a single metric by which the suitability of a given ECC can be measured. First, we give a brief introduction to the topic, followed by a detailed description of the background of the ECCs and fuzzy extractors studied. Then, we summarise related work and describe an implementation of the ECCs under consideration. Finally, we carry out the actual comparison of the ECCs and the thesis concludes with a summary of the results and suggestions for future work. N2 - Diese Arbeit befasst sich mit Fuzzy Extractors, Sicherheitsprimitiven, die häufig in Verbindung mit Physical Unclonable Functions (PUFs) verwendet werden. Ein Fuzzy Extractor arbeitet in zwei Phasen: Der Generierungsphase und der Reproduktionsphase. In der Generierungsphase wird ein Fehlerkorrekturverfahren (ECC) verwendet, um redundante Bits für eine gegebene PUF-Antwort zu berechnen, die dann als Hilfsdaten gespeichert werden, und ein Schlüssel wird aus der Antwort extrahiert. In der Reproduktionsphase kann dann eine andere (möglicherweise verrauschte) PUF-Antwort zusammen mit diesen Hilfsdaten verwendet werden, um den ursprünglichen Schlüssel zu extrahieren. Es ist klar, dass die Leistung des Fuzzy Extractors stark von der Leistung des zugrunde liegenden ECC abhängt. Daher ist es unerlässlich, ECCs in Verbindung mit Fuzzy Extractors zu vergleichen, um sie für eine bestimmte Situation so geeignet wie möglich zu machen. Es ist wichtig, darauf hinzuweisen, dass es aufgrund der Vielzahl verschiedener PUFs mit unterschiedlichen Eigenschaften sehr unrealistisch ist, eine einzige Metrik vorzuschlagen, mit der die Eignung eines bestimmten ECCs gemessen werden kann. Wir beginnen mit einer kurzen Einführung in das Thema, gefolgt von einer detaillierten Beschreibung des Hintergrunds der untersuchten ECCs und Fuzzy Extractors. Anschließend fassen wir verwandte Arbeiten zusammen und beschreiben eine Implementierung der untersuchten ECCs. Schließlich führen wir den eigentlichen Vergleich der ECCs durch und schließen die Arbeit mit einer Zusammenfassung der Ergebnisse und Vorschlägen für zukünftige Arbeiten ab. T2 - Ein umfassender Vergleich von Fuzzy Extractors unter Verwendung verschiedener Fehlerkorrekturverfahren KW - Fuzzy extractor KW - Error correction KW - Vorwärtsfehlerkorrektur KW - Codierungstheorie KW - Physical unclonable function KW - Biometrie Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-12914 VL - 2023 ER - TY - THES A1 - Welearegai, Gebrehiwet Biyane T1 - Precise Detection of Injection Attacks in Real-world Applications N2 - Code injection attacks like the one used in the high-profile 2017 Equifax breach, have become increasingly common, ranking at the top of OWASP’s list of critical web application vulnerabilities. The injection attacks can also target embedded applications running on processors like ARM and Xtensa by exploiting memory bugs and maliciously altering the program’s behavior or even taking full control over a system. Especially, ARM’s support of low power consumption without sacrificing performance is leading the industry to shift towards ARM processors, which advances the attention of injection attacks as well. In this thesis, we are considering web applications and embedded applications (running on ARM and Xtensa processors) as the target of injection attacks. To detect injection attacks in web applications, taint analysis is mostly proposed but the precision, scalability, and runtime overhead of the detection depend on the analysis types (e.g., static vs dynamic, sound vs unsound). Moreover, in the existing dynamic taint tracking approach for Java- based applications, even the most performant can impose a slowdown of at least 10–20% and often far more. On the other hand, considering the embedded applications, while some initial research has tried to detect injection attacks (i.e., ROP and JOP) on ARM, they suffer from high performance or storage overhead. Besides, the Xtensa has been neglected though used in most firmware-based embedded WiFi home automation devices. This thesis aims to provide novel approaches to precisely detect injection attacks on both the web and embedded applications. To that end, we evaluate JavaScript static analysis frameworks to evaluate the security of a hybrid app (JS & native) from an industrial partner, provide RIVULET – a tool that precisely detects injection attacks in Java-based real-world applications, and investigate injection attacks detection on ARM and Xtensa platforms using hardware performance counters (HPCs) and machine learning (ML) techniques. To evaluate the security of the hybrid application, we initially compare the precision, scalability, and code coverage of two widely-used static analysis frameworks—WALA and SAFE. The result of our comparison shows that SAFE provides higher precision and better code coverage at the cost of somewhat lower scalability. Based on these results, we analyze the data flows of the hybrid app via taint analysis by extending the SAFE’s taint analysis and detected a potential for injection attacks of the hybrid application. Similarly, to detect injection attacks in Java-based applications, we provide Rivulet which monitors the execution of developer-written functional tests using dynamic taint tracking. Rivulet uses a white-box test generation technique to re-purpose those functional tests to check if any vulnerable flow could be exploited. We compared Rivulet to the state-of-the-art static vulnerability detector Julia on benchmarks and Rivulet outperformed Julia in both false positives and false negatives. We also used Rivulet to detect new vulnerabilities. Moreover, for applications running on ARM and Xtensa platforms, we investigate ROP1 attack detection by combining HPCs and ML techniques. We collect data exploiting real- world vulnerable applications and small benchmarks to train the ML. For ROP attack detection on ARM, we also implement an online monitor which labels a program’s execution as benign or under attack and stops its execution once the latter is detected. Evaluating our ROP attack detection approach on ARM provides a detection accuracy of 92% for the offline training and 75% for the online monitoring. Similarly, our ROP attack detection on the firmware-only Xtensa processor provides an overall average detection accuracy of 79%. Last but not least, this thesis shows how relevant taint analysis is to precisely detect injection attacks on web applications and the power of HPC combined with machine learning in the control flow injection attacks detection on ARM and Xtensa platforms. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-12926 ER - TY - RPRT A1 - Eckhardt, Dennis A1 - Freiling, Felix A1 - Herrmann, Dominik A1 - Katzenbeisser, Stefan A1 - Pöhls, Henrich C. T1 - Sicherheit in der Digitalisierung des Alltags: Definition eines ethnografisch-informatischen Forschungsfeldes für die Lösung alltäglicher Sicherheitsprobleme N2 - In den vergangenen Jahrzehnten hat es unübersehbar zahlreiche Fortschritte im Bereich der IT-Sicherheitsforschung gegeben, etwa in den Bereichen Systemsicherheit und Kryptographie. Es ist jedoch genauso unübersehbar, dass IT-Sicherheitsprobleme im Alltag der Menschen fortbestehen. Mutmaßlich liegt dies an der Komplexität von Alltagssituationen, in denen Sicherheitsmechanismen und Gerätefunktionalität sowie deren Heterogenität in schwer antizipierbarer Weise mit menschlichem Verständnis und Alltagsgebrauch interagieren. Um die wissenschaftliche Forschung besser auf Menschen und deren IT-Sicherheitsbedürfnisse auszurichten, müssen wir daher den Alltag der Menschen besser verstehen. Das Verständnis von Alltag ist in der Informatik jedoch noch unterentwickelt. Dieser Beitrag möchte das Forschungsfeld “Sicherheit in der Digitalisierung des Alltags” definieren, um Forschenden die Gelegenheit zu geben, ihre Anstrengungen in diesem Bereich zu bündeln. Wir machen dabei Vorschläge einerseits zur inhaltlichen Eingrenzung der informatischen Forschung. Andererseits möchten wir durch die Einbeziehung von Forschungsmethoden aus der Ethnografie, die Erkenntnisse aus der durchaus subjektiven Beobachtung des “Alltags” vieler einzelner Individuen zieht, zur methodischen Weiterentwicklung interdisziplinärer Forschung in diesem Feld beitragen. Die IT- Sicherheitsforschung kann dann Bestehendes gezielt für eine richtige Alltagstauglichkeit optimieren und neue grundlegende Sicherheitsfunktionalitäten für die konkreten Herausforderungen im Alltag entwickeln. KW - Alltagsdigitalisierung KW - Ethnografie KW - IT-Sicherheit KW - Interdisziplinarität Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-13721 ER - TY - THES A1 - Danner, Dominik T1 - Towards Quality of Service and Fairness in Smart Grid Applications N2 - Due to the increasing amount of distributed renewable energy generation and the emerging high demand at consumer connection points, e. g., electric vehicles, the power distribution grid will reach its capacity limit at peak load times if it is not expensively enhanced. Alternatively, smart flexibility management that controls user assets can help to better utilize the existing power grid infrastructure for example by sharing available grid capacity among connected electric vehicles or by disaggregating flexibility requests to hybrid photovoltaic battery energy storage systems in households. Besides maintaining an acceptable state of the power distribution grid, these smart grid applications also need to ensure a certain quality of service and provide fairness between the individual participants, both of which are not extensively discussed in the literature. This thesis investigates two smart grid applications, namely electric vehicle charging-as-a-service and flexibility-provision-as-a-service from distributed energy storage systems in private households. The electric vehicle charging service allocation is modeled with distributed queuing-based allocation mechanisms which are compared to new probabilistic algorithms. Both integrate user constraints (arrival time, departure time, and energy required) to manage the quality of service and fairness. In the queuing-based allocation mechanisms, electric vehicle charging requests are packetized into logical charging current packets, representing the smallest controllable size of the charging process. These packets are queued at hierarchically distributed schedulers, which allocate the available charging capacity using the time and frequency division multiplexing technique known from the networking domain. This allows multiple electric vehicles to be charged simultaneously with variable charging currents. To achieve high quality of service and fairness among electric vehicle charging processes, dynamic weights are introduced into a weighted fair queuing scheduler that considers electric vehicle departure time and required energy for prioritization. The distributed probabilistic algorithms are inspired by medium access protocols from computer networking, such as binary exponential backoff, and control the quality of service and fairness by adjusting sampling windows and waiting periods based on user requirements. The second smart grid application under investigation aims to provide flexibility provision-as-a-service that disaggregates power flexibility requests to distributed battery energy storage systems in private households. Commonly, the main purpose of stationary energy storage is to store energy from a local photovoltaic system for later use, e. g., for overnight charging of an electric vehicle. This is optimized locally by a home energy management system, which also allows the scheduling of external flexibility requests defined by the deviation from the optimal power profile at the grid connection point, for example, to perform peak shaving at the transformer. This thesis discusses a linear heuristic and a meta heuristic to disaggregate a flexibility request to the single participating energy management systems that are grouped into a flexibility pool. Thereby, the linear heuristic iteratively assigns portions of the power flexibility to the most appropriate energy management system for one time slot after another, minimizing the total flexibility cost or maximizing the probability of flexibility delivery. In addition, a multi-objective genetic algorithm is proposed that also takes into account power grid aspects, quality of service, and fairness among par-ticipating households. The genetic operators are tailored to the flexibility disaggregation search space, taking into account flexibility and energy management system constraints, and enable power-optimized buffering of fitness values. Both smart grid applications are validated on a realistic power distribution grid with real driving patterns and energy profiles for photovoltaic generation and household consumption. The results of all proposed algorithms are analyzed with respect to a set of newly defined metrics on quality of service, fairness, efficiency, and utilization of the power distribution grid. One of the main findings is that none of the tested algorithms outperforms the others in all quality of service metrics, however, integration of user expectations improves the service quality compared to simpler approaches. Furthermore, smart grid control that incorporates users and their flexibility allows the integration of high-load applications such as electric vehicle charging and flexibility aggregation from distributed energy storage systems into the existing electricity distribution infrastructure. However, there is a trade-off between power grid aspects, e. g., grid losses and voltage values, and the quality of service provided. Whenever active user interaction is required, means of controlling the quality of service of users’ smart grid applications are necessary to ensure user satisfaction with the services provided. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-13731 ER - TY - THES A1 - Fink, Simon Dominik T1 - Constrained Planarity Algorithms in Theory and Practice N2 - In the constrained planarity setting, we ask whether a graph admits a crossing-free drawing that additionally satisfies a given set of constraints. These constraints are often derived from very natural problems; prominent examples are Level Planarity, where vertices have to lie on given horizontal lines indicating a hierarchy, Partially Embedded Planarity, where we extend a given drawing without modifying already-drawn parts, and Clustered Planarity, where we additionally draw the boundaries of clusters which recursively group the vertices in a crossing-free manner. In the last years, the family of constrained planarity problems received a lot of attention in the field of graph drawing. Efficient algorithms were discovered for many of them, while a few others turned out to be NP-complete. In contrast to the extensive theoretical considerations and the direct motivation by applications, only very few of the found algorithms have been implemented and evaluated in practice. The goal of this thesis is to advance the research on both theoretical as well as practical aspects of constrained planarity. On the theoretical side, we consider two types of constrained planarity problems. The first type are problems that individually constrain the rotations of vertices, that is they restrict the counter-clockwise cyclic orders of the edges incident to vertices. We give a simple linear-time algorithm for the problem Partially Embedded Planarity, which also generalizes to further constrained planarity variants of this type. The second type of constrained planarity problem concerns more involved planarity variants that come down to the question whether there are embeddings of one or multiple graphs such that the rotations of certain vertices are in sync in a certain way. Clustered Planarity and a variant of the Simultaneous Embedding with Fixed Edges Problem (Connected SEFE-2) are well-known problems of this type. Both are generalized by our Synchronized Planarity problem, for which we give a quadratic algorithm. Through reductions from various other problems, we provide a unified modelling framework for almost all known efficiently solvable constrained planarity variants that also directly provides a quadratic-time solution to all of them. For both our algorithms, a key ingredient for reaching an efficient solution is the usage of the right data structure for the problem at hand. In this case, these data structures are the SPQR-tree and the PC-tree, which describe planar embedding possibilities from a global and a local perspective, respectively. More specifically, PC-trees can be used to locally describe the possible cyclic orders of edges around vertices in all planar embeddings of a graph. This makes it a key component for our algorithms, as it allows us to test planarity while also respecting further constraints, and to communicate constraints arising from the surrounding graph structure between vertices with synchronized rotation. Bridging over to the practical side, we present the first correct implementation of PC-trees. We also describe further improvements, which allow us to outperform all implementations of alternative data structures (out of which we only found very few to be fully correct) by at least a factor of 4. We show that this yields a simple and competitive planarity test that can also yield an embedding to certify planarity. We also use our PC-tree implementation to implement our quadratic algorithm for solving Synchronized Planarity. Here, we show that our algorithm greatly outperforms previous attempts at solving related problems like Clustered Planarity in practice. We also engineer its running time and show how degrees of freedom in the theoretical algorithm can be leveraged to yield an up to tenfold speed-up in practice. KW - Constrained Planarity KW - Clustered Planarity KW - Synchronized Planarity KW - Algorithm Engineering Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-13817 ER -