004 Datenverarbeitung; Informatik
Refine
Year of publication
Document Type
- Doctoral Thesis (104)
- Conference Proceeding (7)
- Article (1)
- Master's Thesis (1)
- Other (1)
- Preprint (1)
Has Fulltext
- yes (115)
Keywords
- Graphenzeichnen (7)
- Computersicherheit (6)
- Software Engineering (6)
- Graph (5)
- Multimedia (5)
- Programmanalyse (5)
- Information Retrieval (4)
- Modellierung (4)
- Semantic Web (4)
- Abfrageverarbeitung (3)
Institute
- Fakultät für Informatik und Mathematik (55)
- Mitarbeiter Lehrstuhl/Einrichtung der Fakultät für Informatik und Mathematik (50)
- Sonstiger Autor der Fakultät für Informatik und Mathematik (8)
- Mitarbeiter Lehrstuhl/Einrichtung der Wirtschaftswissenschaftlichen Fakultät (2)
- Institut für IT-Sicherheit und Sicherheitsrecht (ISL) (1)
The recent development of a whole plethora of new wireless technologies, such as IEEE 802.11, IEEE 802.15, IEEE 802.16, UMTS, and more recently LTE, etc, has triggered several efforts to integrate these technologies in a converged world of transparent and ubiquitous wireless connectivity. Most of these technologies have evolved around a certain use case and with some user behaviour being assumed; however, there still lacks a holistic solution to adapt access to user needs, in an automatic and transparent manner. One major problem that has to be addressed first, is mobility management between heterogeneous wireless networks. Current mobility management solutions mostly originate from cellular networking systems, which are operator specific, centralised, and focused on a single link technology. In order to deal with the wireless diversity of future wireless and mobile Internet, a new approach is needed. Adaptive wireless connectivity that is tailored around the user needs and capabilities is named context-aware mobility management. Context refers to the information describing the surroundings of the user as well as his/her behaviour, and additional semantic information that could optimise the adaption process. Context management normally entails discovering and tracking context, reasoning based on the discovered information, then adapting (or acting) upon the context-aware application or system. This context management chain is adapted throughout the thesis to the task of context-aware mobility management. The added complexity is necessary to adapt the ubiquitous access to the condition of both the user and the surrounding networks, while assuming that overlapping wireless networks could still be managed in separate management domains. Linking these management domains and aggregating this composite information in the form of a network context is one of the major contributions of this work. An overlay-based solution takes into account this scattered nature of the context management system, which is modelled as a decentralised dynamic location-based service. The proposed architecture is generalised to support ubiquitous location-based services, and a design methodology is proposed to ensure the localised impact of mobility-led context retrieval overhead.
The Sugiyama framework proposed in the seminal paper of 1981 is one of the most important algorithms in graph drawing and is widely used for visualizing directed graphs. In its common version, it draws graphs hierarchically and, hence, maps the topological direction to a geometric direction. However, such a hierarchical layout is not possible if the graph contains cycles, which have to be destroyed in a preceding step. In certain application and problem settings, e.g., bio sciences or periodic scheduling problems, it is important that the cyclic structure of the input graph is preserved and clearly visible in drawings. Sugiyama et al. also suggested apart from the nowadays standard horizontal algorithm a cyclic version they called recurrent hierarchies. However, this cyclic drawing style has not received much attention since. In this thesis we consider such cyclic drawings and investigate the Sugiyama framework for this new scenario. As our goal is to visualize cycles directly, the first phase of the Sugiyama framework, which is concerned with removing such cycles, can be neglected. The cyclic structure of the graph leads to new problems in the remaining phases, however, for which solutions are proposed in this thesis. The aim is a complete adaption of the Sugiyama framework for cyclic drawings. To complement our adaption of the Sugiyama framework, we also treat the problem of cyclic level planarity and present a linear time cyclic level planarity testing and embedding algorithm for strongly connected graphs.
Increased usage and integration of state-of-the-art information technology in our everyday work life aims at increasing the working efficiency. Due to unhandy human-computer-interaction methods this progress does not always result in increased efficiency, for mobile workers in particular. Activity recognition based contextual computing attempts to balance this interaction deficiency. This work investigates wearable, on-body sensing techniques on their applicability in the field of human activity recognition. More precisely we are interested in the spotting and recognition of so-called manipulative hand gestures. In particular the thesis focuses on the question whether the widely used motion sensing based approach can be enhanced through additional information sources. The set of gestures a person usually performs on a specific place is limited -- in the contemplated production and maintenance scenarios in particular. As a consequence this thesis investigates whether the knowledge about the user's hand location provides essential hints for the activity recognition process. In addition, manipulative hand gestures -- due to their object manipulating character -- typically start in the moment the user's hand reaches a specific place, e.g. a specific part of a machinery. And the gestures most likely stop in the moment the hand leaves the position again. Hence this thesis investigates whether hand location can help solving the spotting problem. Moreover, as user-independence is still a major challenge in activity recognition, this thesis investigates location context as a possible key component in a user-independent recognition system. We test a Kalman filter based method to blend absolute position readings with orientation readings based on inertial measurements. A filter structure is suggested which allows up-sampling of slow absolute position readings, and thus introduces higher dynamics to the position estimations. In such a way the position measurement series is made aware of wrist motions in addition to the wrist position. We suggest location based gesture spotting and recognition approaches. Various methods to model the location classes used in the spotting and recognition stages as well as different location distance measures are suggested and evaluated. In addition a rather novel sensing approach in the field of human activity recognition is studied. This aims at compensating drawbacks of the mere motion sensing based approach. To this end we develop a wearable hardware architecture for lower arm muscular activity measurements. The sensing hardware based on force sensing resistors is designed to have a high dynamic range. In contrast to preliminary attempts the proposed new design makes hardware calibration unnecessary. Finally we suggest a modular and multi-modal recognition system; modular with respect to sensors, algorithms, and gesture classes. This means that adding or removing a sensor modality or an additional algorithm has little impact on the rest of the recognition system. Sensors and algorithms used for spotting and recognition can be selected and fine-tuned separately for each single activity. New activities can be added without impact on the recognition rates of the other activities.
With the rise of manycore processors, parallelism is becoming a mainstream necessity. Unfortunately, parallel programming is inherently more difficult than sequential programming; therefore, techniques for automatic parallelisation will become indispensable. We aim at extending the well-known polyhedron model, which promises this automation, beyond some of its current restrictions. Up to now, loop bounds and array subscripts in the modelled codes must be expressions linear in both the variables and the parameters. We lift this restriction and allow certain polynomial expressions instead of linear ones. With our extensions, we are able to handle more programs in all phases of the parallelisation process (dependence analysis, transformation of the program model, code generation). We extend Banerjee's classical dependence analysis to handle one non-linear parameter p, i.e., we are able to determine precisely the solutions of the system of conflict equalities for input programs with non-linear array accesses like A[p*i] in dependence of the residue class of p. We make contributions to three transformations desirable in automatic parallelisation. First, we show that using a generalised Simplex algorithm, which we have developed, schedules with non-linear parameters like theta(i)=floor(i/n) can be computed. In addition, such schedules can be expressed easily as a quantifier elimination problem but this approach turns out to be computationally less efficient with the available implementation. As a second transformation, we study parametric tiling which is used to adapt a parallelised program to the number of available processors at run time. Third, we present a localisation technique to exploit scratchpad memories on architectures on which data caching has to be handled by software. We transform a given code such that it keeps values which are reused in successive iterations of a sequential loop in the scratchpad. An access to a value written in an earlier iteration is served from the scratchpad to accelerate the access. In general, this transformation introduces non-linear loop bounds in the transformed model. Finally, we present an algorithm for generating code for arbitrary semi-algebraic iteration sets, i.e., for iteration sets described by polynomial inequalities in the variables and parameters. This is a vast generalisation of existing polyhedral code generation techniques. Although our algorithm is less efficient than polyhedral code generators, this paves the way for a code generator that can handle arbitrary parametric tilings and other transformations which introduce non-linear parameters (like non-linear schedules and the localisation we present) or even non-linear variables.
Unverkettbare Nachrichten sind ein Grundbaustein anonymer Kommunikation. Anonymisierungsnetze schützen mittels Unverkettbarkeit, wer mit wem kommuniziert sowie die Identität der Beteiligten einer Kommunikationsbeziehung. Anonymisierungsnetze benötigen Kooperation, da die Anonymität durch Ressourcen anderer Teilnehmer geschützt wird. Wenn die Kosten und der Nutzen eines Anonymisierungsnetzes transparent sind, ergeben sich Zielkonflikte zwischen rationalen Teilnehmern. Es wird daher untersucht, inwiefern daraus resultierendes egoistisches Verhalten die Widerstandsfähigkeit dieser Netze beeinträchtigt. Störungen werden in einem spieltheoretischen Modell untersucht, um widerstandsfähige Konfigurationen von Anonymisierungsnetzen zu ermitteln. Eine weitere Störquelle sind Überflutungsangriffe mittels unverkettbarer Nachrichten. Es soll sowohl die Verfügbarkeit als auch die Anonymität geschützt werden. Dazu wird Unverkettbarkeit für Nachrichten aufrecht erhalten, außer wenn die Senderate eines Nachrichtenstroms eine Richtlinie überschreitet. Innerhalb verkettbarer Nachrichten können Überflutungsangriffe erkannt werden. Darüber kann die Verfügbarkeit des Netzdienstes geschützt werden.
The thesis proposes a new formal framework for checking the content of web documents along individual reading paths. It is vital for the readability of web documents that their content is consistent and coherent along the possible browsing paths through the document. Manually ensuring the coherence of content along the possibly huge number of different browsing paths in a web document is time-consuming and error-prone. Existing methods for document validation and verification are not sufficiently expressive and efficient. The innovative core idea of this thesis is to combine the temporal logic CTL and description logic ALC for the representation of consistency criteria. The resulting new temporal description logics ALCCTL can - in contrast to existing specification formalisms - compactly represent coherence criteria on documents. Verification of web documents is modelled as a model checking problem of ALCCTL. The decidability and polynomial complexity of the ALCCTL model checking problem is proven and a sound, complete, and optimal model checking algorithm is presented. Case studies on real and realistic web documents demonstrate the performance and adequacy of the proposed methods. Existing methods such as symbolic model checking or XML-based document validation are outperformed in both expressiveness and speed.
A safe basis for automatic loop parallelization is the polyhedron model which represents the iteration domain of a loop nest as a polyhedron in $\mathbb{Z}^n$. However, turning the parallel loop program in the model to efficient code meets with several obstacles, due to which performance may deteriorate seriously -- especially on distributed memory architectures. We introduce a fine-grained model of the computation performed and show how this model can be applied to create efficient code.
Computerunterstützte Beratungssysteme finden sowohl in der Industrie als auch im akademischen Bereich eine zunehmende Bedeutung. Die Anforderungen an solche Systeme sind hinsichtlich der abbildbaren Strukturen, der Flexibilität der Anfragen und der Vollständigkeit und Korrektheit der Antworten hoch. Dies gilt insbesondere für Planungsprobleme in strukturierten Domänen. Derartige Probleme treten beispielsweise bei der Erstellung von Tests auf der Grundlage einer Menge von Fragen und gewissen Anforderungen an den Test, bei der Konsistenzprüfung von Studienordnungen und bei der computerunterstützten Studienberatung auf. In der vorliegenden Arbeit wird ein Framework zur Behandlung eben genannter Probleme präsentiert. Die vorgestellte Lösung bietet durch den modellbasierten Ansatz und die entwickelte anwendungsnahe Modellierungssprache – gerade auch im Vergleich zu existierenden Ansätzen – einen sehr hohen Grad an Abstraktion, Allgemeingültigkeit, Ausdrucksstärke, Flexibilität und Integrierbarkeit. Im Rahmen des entwickelten Modells wird eine geeignete Verzahnung von strukturellen und constraintbasierten Aspekten erreicht. Der hierbei in Syntax und Semantik definierte Constraintbegriff kann darüber hinaus als Formalisierung und Verallgemeinerung von Pfadconstraints bzw. Pfadanfragen in hierarchischen Datenmodellen aufgefasst werden. Für die interne Repräsentation erweist sich ein logikbasierter Ansatz mit Constraints, nämlich Answer Set Programming mit Gewichten, als eine ausgezeichnete Methode bezüglich der Ausdrucksstärke, Mächtigkeit und Adäquatheit. Die Praxistauglichkeit des verfolgten Ansatzes im Hinblick auf Performanz und Skalierbarkeit wird in verschiedenen realen Anwendungsfällen demonstriert.
Die vorliegende Arbeit befaßt sich mit der dreidimensionalen Rekonstruktion reflektierender Oberflächen. Dabei wird sowohl die Oberflächenform als auch die absolute Lage im Raum bestimmt. Es werden Oberflächen behandelt, die einerseits total reflektieren, andererseits diffuse und spiegelnde Reflexionsanteile aufweisen. Zur Lösung des Problems werden zwei Kameras und mehrere Lichtquellen verwendet. Eine genauere Analyse der Lichtreflexion an spiegelnden Objekten führt zu einer Beschreibung des Problems als Lösung einer totalen Differentialgleichung. Diese Lösung wird als Startwert für die Rekonstruktion partiell reflektierender Oberflächen verwendet.
Aspect-Oriented Programming (AOP) has been promoted as a solution for modularization problems known as the tyranny of the dominant decomposition in literature. However, when analyzing AOP languages it can be doubted that uncontrolled AOP is indeed a silver bullet. The contributions of the work presented in this thesis are twofold. First, we critically analyze AOP language constructs and their effects on program semantics to sensitize programmers and researchers to resulting problems. We further demonstrate that AOP—as available in AspectJ and similar languages—can easily result in less understandable, less evolvable, and thus error prone code—quite opposite to its claims. Second, we examine how tools relying on both static and dynamic program analysis can help to detect problematical usage of aspect-oriented constructs. We propose to use change impact analysis techniques to both automatically determine the impact of aspects and to deal with AOP system evolution. We further introduce an analysis technique to detect potential semantical issues related to undefined advice precedence. The thesis concludes with an overview of available open source AspectJ systems and an assessment of aspect-oriented programming considering both fundamentals of software engineering and the contents of this thesis.