@phdthesis{Hanning2002, author = {Hanning, Tobias}, title = {Vektorielle Mehrniveaupassung. Anwendungen in der Bildsegmentierung}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-295}, school = {Universit{\"a}t Passau}, year = {2002}, abstract = {Die Anwendungen der vektoriellen Mehrniveaupassung in der Bildsegmentierung stehen in unmittelbarer Nachbarschaft zum verbreiteten Ansatz, Bilder mit Methoden der Variationsrechnung {\"u}ber einen Energieterm zu segmentieren. Beiden Verfahren ist gemeinsam, daß sie versuchen, das gegebene Bild durch st{\"u}ckweise stetige Funktionen zu approximieren. Die maximalen Teilmengen des Definitionsbereichs, auf denen die approximierende Funktion stetig ist, bilden dann die Segmente. Im Gegensatz zu dem in der Literatur h{\"a}ufig unter dem Schlagwort Mumford-Shah-Modell bekannten Energieminimierungsverfahren ist der Raum der Funktionen, mit denen das Bild approximiert wird, bei der vektoriellen Mehrniveaupassung ein endlicher Vektorraum. Ein weiterer Unterschied zu diesem Ansatz ist das System der erlaubten Mengen. Es werden nur Segmentierungen erlaubt, deren Segmente aus diesem Mengensystem sind. Die durch diese Einschr{\"a}nkung schlankere Theorie f{\"u}hrt zu einer gesicherten Existenz einer optimalen L{\"o}sung des Segmentierungsproblems, die der g{\"a}ngigen Vorstellung einer Segmentierung gen{\"u}gt. Die Berechnung lokaler Optima ist algorithmisch innerhalb der Theorie umsetzbar.}, subject = {Bildsegmentierung}, language = {de} } @phdthesis{Fischer2001, author = {Fischer, Bernd}, title = {Deduction-Based Software Component Retrieval}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-231}, school = {Universit{\"a}t Passau}, year = {2001}, abstract = {Deduction-based software component retrieval is a software reuse technique that uses formal specifications as component descriptors and as search keys; matching components are identified using an automated theorem prover. This dissertation contains a detailed theoretical investigation of the concept as well as the first substantial experimental evaluation of its technical feasibility.}, subject = {Software engineering}, language = {en} } @phdthesis{Braumandl2002, author = {Braumandl, Reinhard}, title = {Quality of Service and Optimization in Data Integration Systems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-279}, school = {Universit{\"a}t Passau}, year = {2002}, abstract = {This work presents techniques for the construction of a global data integrations system. Similar to distributed databases this system allows declarative queries in order to express user-specific information needs. Scalability towards global data integration systems and openness were major design goals for the architecture and techniques developed in this work. It is shown how service composition, extensibility and quality of service can be supported in an open system of providers for data, functionality for query processing operations, and computing power.}, subject = {Dienstg{\"u}te}, language = {en} } @phdthesis{MianSyed2001, author = {Mian Syed, Alexandra}, title = {Engineering wissensbasierter Navigation und Steuerung autonom-mobiler Systeme}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-159}, school = {Universit{\"a}t Passau}, year = {2001}, abstract = {Die autonome Steuerung mobiler, technischer Systeme in nicht exakt vorherbestimmbaren Situationen erfordert Methoden der autonomen Entscheidungsfindung, um ein planvolles, zielgerichtetes Agieren und Reagieren unter Echtzeitbedingungen realisieren zu k{\"o}nnen. W{\"a}hrend mittels mathematischer Formeln Basisverhalten, wie beispielsweise in einer Geradeausbewegung, einer Drehung, bei einem Abbremsen, und in Gefahrenmomenten schnelle Reaktionen, berechnet werden, ben{\"o}tigt man auf der anderen Seite ein Regelsystem, um dar{\"u}ber hinaus "intelligentes", d.h. situationsangepaßtes Verhalten zu produzieren und gleichzeitig im Hinblick auf ein Missionsziel planvoll agieren zu k{\"o}nnen. Derartige Regelsysteme m{\"u}ssen sich auf einer abstrakten Ebene formulieren lassen, sollen sie vom Menschen problemlos entwickelbar, leicht modifizierbarund gut verifizierbar bleiben. Eine aufgrund ihres Konzeptes geeignete Programmierwelt ist die Logikprogrammierung. Ziel der Logikprogrammierung ist es weniger, Arbeitsabl{\"a}ufe zu beschreiben, als vielmehr Wissen in Form von Fakten zu spezifizieren und mit Hilfe von Regeln Schlußfolgerungen aus diesen Fakten ziehen zu k{\"o}nnen. Die klassische Logikprogrammierung ist jedoch aufgrund ihres Auswertungsmechanismus der SLD-Resolution (linear resolution with selected function for definite clauses) zu langsam f{\"u}r die Anwendung bei Echtzeitsystemen. Auch parallele Sprachformen, die ebenfalls mit SLD-Resolution arbeiten, erreichen beim Einsatz auf (von Neumann-) Mehrprozessorsystemen bislang nicht die notwendige Effizienz. Das Anwendungsgebiet der deduktiven Datenbanken hat im Vergleich dazu durch Bottom-Up Techniken einen anderen Auswertungsansatz mit deutlich h{\"o}herer Effizienz geliefert. Viele dort auftretenden Probleme k{\"o}nnen jedoch nur durch die Integration anforderungsgetriebener Abarbeitung gel{\"o}st werden. Auf der anderen Seite stellen Datenflußrechnerarchitekturen aufgrund der automatisierten Ausbeutung feink{\"o}rniger Parallelit{\"a}t einen hervorragenden Ansatz der Parallelverarbeitung dar. Bei Datenflußrechnerarchitekturen handelt es sich um (Mehrprozessor-) Systeme, deren datengetriebener Abarbeitungsmechanismus sich grundlegend vom weit verbreiteten kontrollflußgesteuerten von Neumann-Prinzip unterscheidet.{\"U}berlegungen zur Struktur von Steuerungssystemen werden ergeben, daß es mittels Ans{\"a}tzen aus dem Gebiet der deduktiven Datenbanken m{\"o}glich ist, ein f{\"u}r diese Aufgabenstellung neuartiges, ausschließlich datengetriebenes Auswertungsmodell zu generieren. Dabei vermeidet es Probleme, die bei Bottom-Up Verfahren auftreten k{\"o}nnen, wie z.B. das Auftreten unendlicher Wertemengen und die sp{\"a}te Einschr{\"a}nkung auf relevante Werte, ohne gleichzeitig die Stratifizierung von Programmen zu gef{\"a}hrden. Ergebnis der Arbeit ist eine anwendungsbezogene, problemorientierte Entwicklungsumgebung, die einerseits die Entwicklung und Verifikation der Spezifikation mit existierenden Werkzeugen erlaubt und andererseits die effiziente, parallele Ausf{\"u}hrung auf geeigneten Rechensystemen erm{\"o}glicht. Zus{\"a}tzlich wird die Voraussetzung geschaffen, verschiedene weitere, f{\"u}r die Steuerung autonomer Systeme unverzichtbare Komponenten in das Abarbeitungsmodell zu integrieren. Simulationsergebnisse werden belegen, daß das vorgestellte Berechnungsmodell bez{\"u}glich realer Anwendungsbeispiele bereits in einer Monoprozessorversion Echtzeitbedingungen gen{\"u}gt. Damit ist die Voraussetzung f{\"u}r die Ausf{\"u}hrung zuk{\"u}nftiger, weitaus komplexerer Steuerungsprobleme, ggf. auf Mehrprozessorsystemen, in Echtzeit geschaffen.}, subject = {Autonomer Roboter}, language = {de} } @phdthesis{Bachl2001, author = {Bachl, Sabine}, title = {Isomorphe Subgraphen und deren Anwendung beim Zeichnen von Graphen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-149}, school = {Universit{\"a}t Passau}, year = {2001}, abstract = {In der Arbeit wird der Begriff der Isomorphen Subgraphen definiert. Anschließend werden theoretische und praktische Ergebnisse bei der Erkennung Isomorpher Graphen er{\"o}rtert.}, subject = {Isomorpher Teilgraph}, language = {de} } @phdthesis{Zukowski2001, author = {Zukowski, Ulrich}, title = {Flexible Computation of the Well-Founded Semantics of Normal Logic Programs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-226}, school = {Universit{\"a}t Passau}, year = {2001}, abstract = {The well-founded semantics has been accepted as the most relevant semantics for logic-based information systems. In this dissertation a framework based on a set of program transformations is presented that generalizes all major computation approaches for the well-founded semantics using a common data structure and provides a common language to describe their evaluation strategy. This rewriting system gives the formal background to analyze and combine different evaluation strategies in a common framework, or to design new algorithms and prove the correctness of its implementations at a high level just by changing the order of program transformations.}, subject = {Logische Programmierung}, language = {en} } @phdthesis{Boerncke2000, author = {B{\"o}rncke, Frank}, title = {Modellierung syntaktischer Strukturen nat{\"u}rlicher Sprachen mit Graphgrammatiken}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-28}, school = {Universit{\"a}t Passau}, year = {2000}, abstract = {Die vorliegende Arbeit erschließt durch die Formalisierung einer linguistischen Theorie M{\"o}glichkeiten zum Entwurf generischer Verfahren zur Verarbeitung nat{\"u}rlicher Sprachen. Zu diesem Zweck setzen wir Graphsprachen f{\"u}r die Modellierung syntaktischer Strukturen ein. Damit lassen sich Ergebnisse der linguistischen Forschung mit Begriffen der Graphentheorie beschreiben und bewerten. Zu diesem Ansatz motiviert der Umstand, daß in der Linguistik im Rahmen der Syntax jedem Satz einer nat{\"u}rlichen Sprache eine nichtsequentielle Struktur zugesprochen wird. Diese Struktur {\"u}berlagert die lineare Wortfolge, die wir als Satz kennen. Eine Menge solcher syntaktischen Strukturen die wir mit Graphen modellieren k{\"o}nnen betrachten wir als Graphsprache. Die Arbeit zeigt, wie sich solche Graphsprachen mit Hilfe von Graphgrammatiken beschreiben lassen. Wie alle formalen Sprachen zeichnen sich auch Graphgrammatiken dadurch aus, daß sie mathematisch wohldefniert sind. Dies stellt eine notwendige Voraussetzung dar, um Aussagen {\"u}ber eine Sprache zu beweisen. Von Interesse ist dabei vor allem die Untersuchung unendlicher Mengen. Das Ziel besteht dann darin, f{\"u}r sie eine endliche Beschreibung zu finden. Diese Aufgabe wird in der Regel von einer Grammatik erf{\"u}llt. Dar{\"u}ber hinaus ist man an erkennenden Algorithmen f{\"u}r Sprachen interessiert, die das Wortproblem effizient l{\"o}sen. Bez{\"u}glich nat{\"u}rlicher Sprachen werden beide Aufgabenstellungen in dieser Arbeit mit Hilfe von Graphgrammatiken gel{\"o}st.}, subject = {Graphensprache}, language = {de} } @phdthesis{Wichert2000, author = {Wichert, Carl-Alexander}, title = {ULTRA - A Logic Transaction Programming Language}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-105}, school = {Universit{\"a}t Passau}, year = {2000}, abstract = {Rule-based language for the specification of complex database updates and transactions. Formal treatment of the syntax and the declarative semantics}, subject = {Programmierlogik}, language = {en} } @phdthesis{Dolzmann2000, author = {Dolzmann, Andreas}, title = {Algorithmic strategies for applicable real quantifier elimination}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-64}, school = {Universit{\"a}t Passau}, year = {2000}, abstract = {One of the most important algorithms for real quantifier elimination is the quantifier elimination by virtual substitution introduced by Weispfenning in 1988. In this thesis we present numerous algorithmic approaches for optimizing this quantifier elimination algorithm. Optimization goals are the actual running time of the implementation of the algorithm and the size of the output formula. Strategies for obtaining these goals include simplification of first-order formulas,reduction of the size of the computed elimination set, and condensing a new replacement for the virtual substitution. Local quantifier elimination computes formulas that are equivalent to the input formula only nearby a given point. We can make use of this restriction for further optimizing the quantifier elimination by virtual substitution. Finally we discuss how to solve a large class of scheduling problems by real quantifier elimination. To optimize our algorithm for solving scheduling problems we make use of the special form of the input formula and of additional information given by the description of the scheduling problem}, subject = {Quantorenelimination}, language = {en} } @phdthesis{Urban2004, author = {Urban, Christoph}, title = {Das Referenzmodell PECS - Agentenbasierte Modellierung menschlichen Handelns, Entscheidens und Verhaltens}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-471}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {Die Agententechnologie hat in den letzten Jahren eine rasante Entwicklung erfahren und mittlerweile großen Einfluss auf verschiedene Bereiche in Wissenschaft und Technik genommen. Insbesondere wurde die agentenbasierte Modellbildung und Simulation als wirkungsvolles Mittel f{\"u}r die Untersuchung realer oder hypothetischer Systeme erkannt. Im Vordergrund stehen hierbei ganz besonders Systeme, die durch menschliches Handeln, Entscheiden und Verhalten beeinflusst werden, oder der Mensch selbst, um seine Eigenschaften und F{\"a}higkeiten aus den Blickwinkeln unterschiedlicher wissenschaftlicher Disziplinen heraus weiterf{\"u}hrend zu erforschen. Das prim{\"a}re Ziel der vorliegenden Arbeit besteht darin, den Entwurf agenten-basierter Simulationsmodelle, in denen menschliches Handeln, Entscheiden und Verhalten von ausschlaggebender Bedeutung sind, auf konzeptioneller Ebene zu unterst{\"u}tzen. Um dieses Ziel zu erreichen, wird das dom{\"a}nen- und theorieunabh{\"a}ngige Referenzmodell PECS vorgestellt, das Strukturierungsprinzipien aus der Informatik mit systemtheoretischen Ans{\"a}tzen verbindet, um das Wechselspiel vielf{\"a}ltiger Einflussbereiche auf das menschliche Handeln im Rahmen einer integrativen und umfassenden Agentenarchitektur abzubilden. Auf Grundlage des Referenzmodells werden insgesamt vier charakteristische Fallstudien aus der Psychologie, der Sozialpsychologie, der Soziologie und der experimentellen {\"O}konomie entwickelt, um den Einsatz des Referenzmodells in der Praxis zu demonstrieren.}, subject = {Agent }, language = {de} } @phdthesis{Robschink2004, author = {Robschink, Torsten}, title = {Pfadbedingungen in Abh{\"a}ngigkeitsgraphen und ihre Anwendung in der Softwaresicherheitstechnik}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-469}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {Diese Arbeit pr{\"a}sentiert eine neue Methode zur Sicherheitsanalyse von Software im Bereich der Manipulationspr{\"u}fung und der Einhaltung von Informationsfl{\"u}ssen zwischen verschiedenen Sicherheitsniveaus. Program-Slicing und Constraint-Solving sind eigenst{\"a}ndige Verfahren, die sowohl zur Abh{\"a}ngigkeitsbestimmung als auch zur Berechnung arithmetischer Eigenschaften verwendet werden. Die erstmalige Kombination dieser beiden Verfahren mittels Pfadbedingungen liefert nicht nur bin{\"a}re Abh{\"a}ngigkeitsinformationen wie Slicing, sondern exakte notwendige Bedingungen {\"u}ber die Informationsfl{\"u}sse zwischen zwei Programmpunkten. Neben der Definition der Grundlagen von Abh{\"a}ngigkeitsgraphen und einfachen Pfadbedingungen werden neue Erweiterungen f{\"u}r kontextsensitive interprozedurale Pfadbedingungen gezeigt und die Integration von dom{\"a}nenspezifischen Verfahren f{\"u}r Arrayfelder und abstrakten Datentypen demonstriert. Der Schwerpunkt der Arbeit liegt in der Realisierung von Pfadbedingungen f{\"u}r echte Programme in echten Programmiersprachen. Hierf{\"u}r werden Verfahren vorgeschlagen, realisiert und empirisch untersucht, wie Pfadbedingungen f{\"u}r große Programme skalieren. Die zum Einsatz kommenden Techniken sind u.a. Intervallanalyse und Bin{\"a}re Entscheidungsgraphen, mit denen die generelle exponentielle Komplexit{\"a}t von Pfadbedingungen beherrschbar wird. Fallstudien f{\"u}r den Einsatz von Pfadbedingungen und die empirische Untersuchung mehrerer Verfahren zur Intervallanalyse zeigen, dass Pfadbedingungen f{\"u}r die praktische Programmanalyse und das Programmverstehen geeignet und empfehlenswert sind.}, subject = {Programmanalyse}, language = {de} } @phdthesis{Seidl2006, author = {Seidl, Andreas}, title = {Cylindrical Decomposition Under Application-Oriented Paradigms}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-816}, school = {Universit{\"a}t Passau}, year = {2006}, abstract = {Quantifier elimination (QE) is a powerful tool for problem solving. Once a problem is expressed as a formula, such a method converts it to a simpler, quantifier-free equivalent, thus solving the problem. Particularly many problems live in the domain of real numbers, which makes real QE very interesting. Among the so far implemented methods, QE by cylindrical algebraic decomposition (CAD) is the most important complete method. The aim of this thesis is to develop CAD-based algorithms, which can solve more problems in practice and/or provide more interesting information as output. An algorithm that satisfies these standards would concentrate on generic cases and postpone special and degenerated ones to be treated separately or to be abandoned completely. It would give a solution, which is locally correct for a region the user is interested in. It would give answers, which can provide much valuable information in particular for decision problems. It would combine these methods with more specialized ones, for subcases that allow for. It would exploit degrees of freedom in the algorithms by deciding to proceed in a way that promises to be efficient. It is the focus of this dissertation to treat these challenges. Algorithms described here are implemented in the computer logic system REDLOG and ship with the computer algebra system REDUCE.}, subject = {Quantorenelimination}, language = {en} } @phdthesis{Ellmenreich2004, author = {Ellmenreich, Nils}, title = {PolyAPM: Comparative Parallel Programming with Abstract Parallel Machines}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-447}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {A parallelising compilation consists of many translation and optimisation stages. The programmer may steer the compiler through these stages by supplying directives with the source code or setting compiler switches. However, for an evaluation of the effects of individual stages, their selection and their best order, this approach is not optimal. To solve this problem, we propose the following method. The compilation is cast as a sequence of program transformations. Each intermediate program runs on an Abstract Parallel Machine (APM), while the program generated by the final transformation runs on the target architecture. Our intermediate programs are all in the same language, Haskell. Thus, each program is executable and still abstract enough to be legible, which enables the evaluation of the transformation that generated it. This evaluation is supported by a cost model, which makes a performance prediction of the abstract program for a real machine. Our project, PolyAPM, provides an acyclic directed graph -- usually a tree -- of APMs whose traversal specifies different combinations and orders of transformations. From one source program, several target programs can be constructed. Their run time characteristics can be evaluated and compared. The goal of PolyAPM is not to support the one-off construction of parallel application programs. For the method's overhead to pay off, the project aims rather at supporting the construction and comparison of many similar variations of a parallel program and a comparative evaluation of parallelisation techniques. With the automation of transformations, PolyAPM can also be used to construct semi-automatic compilation systems.}, subject = {Parallelverarbeitung}, language = {en} } @phdthesis{Forster2004, author = {Forster, Michael}, title = {Crossings in Clustered Level Graphs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-481}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {Clustered graphs are an enhanced graph model with a recursive clustering of the vertices according to a given nesting relation. This prime technique for expressing coherence of certain parts of the graph is used in many applications, such as biochemical pathways and UML class diagrams. For directed clustered graphs usually level drawings are used, leading to clustered level graphs. In this thesis we analyze the interrelation of clusters and levels and their influence on edge crossings and cluster/edge crossings.}, subject = {Graphenzeichnen}, language = {en} } @phdthesis{Schreiber2001, author = {Schreiber, Falk}, title = {Visualisierung biochemischer Reaktionsnetze}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-215}, school = {Universit{\"a}t Passau}, year = {2001}, abstract = {In dieser Arbeit werden Anforderungen an die Darstellung biochemischer Reaktionsnetze untersucht und die Netze unter dem Gesichtspunkt der Visualisierung modelliert. Anschliessend wird ein Algorithmus zum Zeichnen biochemischer Reaktionsnetze entwickelt und analysiert.}, subject = {Biochemie}, language = {de} } @phdthesis{Hofmeier2012, author = {Hofmeier, Andreas}, title = {Vergleichen und Aggregieren von partiellen Ordnungen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-26858}, school = {Universit{\"a}t Passau}, year = {2012}, abstract = {Das Vergleichen und Aggregieren von Informationen ist ein zentraler Bereich in der Analyse von Wahlsystemen. In diesen m{\"u}ssen die verschiedenen Meinungen von W{\"a}hlern {\"u}ber eine Menge von Kandidaten zu einem m{\"o}glichst gerechten Wahlergebnis aggregiert werden. In den meisten politischen Wahlen entscheidet sich jeder W{\"a}hler durch Ankreuzen f{\"u}r einen einzigen Kandidaten. Daneben werden aber auch Rangordnungsprobleme als eine Variante von Wahlsystemen untersucht. Bei diesen bringt jeder W{\"a}hler seine Meinung in Form einer totalen Ordnung {\"u}ber der Menge der Kandidaten zum Ausdruck, wodurch seine oftmals komplexe Meinung exakter repr{\"a}sentiert werden kann als durch die Auswahl eines einzigen, favorisierten Kandidaten. Das Wahlergebnis eines Rangordnungsproblems ist dann eine ebenfalls totale Ordnung der Kandidaten, welche die geringste Distanz zu den Meinungen der W{\"a}hler aufweist. Als Distanzmaße zwischen zwei totalen Ordnungen haben sich neben anderen Kendalls Tau-Distanz und Spearmans Footrule-Distanz etabliert. Durch moderne Anwendungsm{\"o}glichkeiten von Rangordnungsproblemen im maschinellen Lernen, in der k{\"u}nstlichen Intelligenz, in der Bioinformatik und vor allem in verschiedenen Bereichen des World Wide Web r{\"u}cken bereits bekannte, jedoch bislang eher wenig studierte Aspekte in den Fokus der Forschung. Zum einen gewinnt die algorithmische Komplexit{\"a}t von Rangordnungsproblemen an Bedeutung. Zum anderen existieren in vielen dieser Anwendungen unvollst{\"a}ndige „W{\"a}hlermeinungen" mit unentschiedenen oder unvergleichbaren Kandidaten, so dass totale Ordnungen zu deren Repr{\"a}sentation nicht l{\"a}nger geeignet sind. Die vorliegende Arbeit greift diese beiden Aspekte auf und betrachtet die algorithmische Komplexit{\"a}t von Rangordnungsproblemen, in denen W{\"a}hlermeinungen anstatt durch totale Ordnungen durch schwache oder partielle Ordnungen repr{\"a}sentiert werden. Dazu werden Kendalls Tau-Distanz und Spearmans Footrule-Distanz auf verschiedene nahe liegende Arten verallgemeinert. Es zeigt sich dabei, dass nun bereits die Distanzberechnung zwischen zwei Ordnungen ein algorithmisch komplexes Problem darstellt. So ist die Berechnung der verallgemeinerten Versionen von Kendalls Tau-Distanz oder Spearmans Footrule-Distanz f{\"u}r schwache Ordnungen noch effizient m{\"o}glich. Sobald jedoch partielle Ordnungen betrachtet werden, sind die Probleme NP-vollst{\"a}ndig, also vermutlich nicht mehr effizient l{\"o}sbar. In diesem Fall werden Resultate zur Approximierbarkeit und zur parametrisierten Komplexit{\"a}t der Probleme vorgestellt. Auch die Komplexit{\"a}t der Rangordnungsprobleme selbst erh{\"o}ht sich. F{\"u}r totale Ordnungen effizient l{\"o}sbare Varianten werden f{\"u}r schwache Ordnungen NP-vollst{\"a}ndig, f{\"u}r totale Ordnungen NP-vollst{\"a}ndige Varianten hingegen liegen f{\"u}r partielle Ordnungen teilweise außerhalb der Komplexit{\"a}tsklasse NP. Die Arbeit schließt mit einem Ausblick auf offene Problemstellungen.}, language = {de} } @phdthesis{Matzeder2012, author = {Matzeder, Marco}, title = {Zeichnen von B{\"a}umen auf Gittern}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-26923}, school = {Universit{\"a}t Passau}, year = {2012}, abstract = {Das Zeichnen von Graphen besch{\"a}ftigt sich mit der Frage, wie die durch einen Graphen repr{\"a}sentierten Informationen f{\"u}r einen Betrachter {\"u}bersichtlich und verst{\"a}ndlich dargestellt werden k{\"o}nnen. Die Graphklasse der B{\"a}ume dient insbesondere zur Repr{\"a}sentation von hierarchischen Strukturen. Neben den hierarchisch und radial darstellenden Verfahren werden B{\"a}ume auch auf dem orthogonalen Gitter gezeichnet, in welchem die Knoten auf ganzzahligen Koordinaten liegen und die Kanten entlang der horizontalen und vertikalen Gitterlinien verlaufen. Gew{\"u}nscht wird eine gute Lesbarkeit der Zeichnungen und deren effiziente Berechnung. F{\"u}r die formale Bewertung der Lesbarkeit existieren speziell f{\"u}r das Zeichnen von B{\"a}umen definierte {\"A}sthetikkriterien, wie eine ebenenweise Darstellung, die Ordnungserhaltung und Kriterien zur Darstellung von Subgraphisomorphien und Symmetrien. Die vorliegende Arbeit befasst sich mit einer bislang wenig studierten Erweiterung des orthogonalen Gitters auf das hexagonale und oktagonale Gitter durch das Hinzunehmen von einer bzw. beider diagonalen Gitterrichtungen, und der Problemstellung, wie B{\"a}ume darauf gezeichnet werden. Dadurch k{\"o}nnen auch B{\"a}ume mit einem h{\"o}heren Grad gezeichnet werden als auf dem orthogonalen Gitter. Die Einschr{\"a}nkung, dass nur B{\"a}ume gezeichnet werden k{\"o}nnen, deren Grad kleiner ist als die Anzahl der Gitterrichtungen des verwendeten Gitters, besteht jedoch weiterhin. Als {\"A}sthetikkriterien werden die lokale Uniformit{\"a}t, die die L{\"a}nge der ausgehenden Kanten eines Knotens festlegt, und Pattern, die deren Richtungen festlegen, eingef{\"u}hrt. Gegen{\"u}ber dem bekannten linearen Fl{\"a}chenverbrauch von geradlinigen Zeichnungen von vollst{\"a}ndigen Bin{\"a}rb{\"a}umen auf dem orthogonalen Gitter, werden f{\"u}r Zeichnungen von vollst{\"a}ndigen d-n{\"a}ren B{\"a}umen mit d > 2 nicht-lineare untere Schranken f{\"u}r die ben{\"o}tigte Fl{\"a}che auf dem hexagonalen und dem oktagonalen Gitter gezeigt. Insgesamt werden f{\"u}r vollst{\"a}ndige und beliebige, geordnete und ungeordnete B{\"a}ume obere und untere Fl{\"a}chenschranken f{\"u}r Zeichnungen auf dem hexagonalen und oktagonalen Gitter pr{\"a}sentiert. Dabei zeigt sich, dass bei nicht-ordnungserhaltenden Zeichnungen zwar mehr als lineare, aber deutlich weniger als quadratische Fl{\"a}che ben{\"o}tigt wird. Im Gegensatz dazu gibt es geordnete B{\"a}ume, deren ordnungserhaltende Zeichnungen exponentielle Fl{\"a}che ben{\"o}tigen. Des Weiteren wird die Ermittlung der minimalen Zeichenfl{\"a}che f{\"u}r geordnete d-n{\"a}re B{\"a}ume ebenso als NP-vollst{\"a}ndig bewiesen, wie das Zeichnen von ungeordneten d-n{\"a}ren B{\"a}umen mit einheitlichen Kantenl{\"a}ngen. Schließlich werden zwei Linearzeitalgorithmen vorgestellt, die geordnete d-n{\"a}re B{\"a}ume unter Einhaltung der genannten {\"A}sthetikkriterien zeichnen.}, subject = {Baum }, language = {de} } @phdthesis{ELKhoury2014, author = {EL-Khoury, Vanessa}, title = {Semantic Protection and Personalization of Video Content. PIAF: MPEG Compliant Adaptation Framework Preserving the User Perceived Quality}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-27360}, school = {Universit{\"a}t Passau}, year = {2014}, abstract = {UME is the notion that a user should receive informative adapted content anytime and anywhere. Personalization of videos, which adapts their content according to user preferences, is a vital aspect of achieving the UME vision. User preferences can be translated into several types of constraints that must be considered by the adaptation process, including semantic constraints directly related to the content of the video. To deal with these semantic constraints, a fine-grained adaptation, which can go down to the level of video objects, is necessary. The overall goal of this adaptation process is to provide users with adapted content that maximizes their Quality of Experience (QoE). This QoE depends at the same time on the level of the user's satisfaction in perceiving the adapted content, the amount of knowledge assimilated by the user, and the adaptation execution time. In video adaptation frameworks, the Adaptation Decision Taking Engine (ADTE), which can be considered as the "brain" of the adaptation engine, is responsible for achieving this goal. The task of the ADTE is challenging as many adaptation operations can satisfy the same semantic constraint, and thus arising in several feasible adaptation plans. Indeed, for each entity undergoing the adaptation process, the ADTE must decide on the adequate adaptation operator that satisfies the user's preferences while maximizing his/her quality of experience. The first challenge to achieve in this is to objectively measure the quality of the adapted video, taking into consideration the multiple aspects of the QoE. The second challenge is to assess beforehand this quality in order to choose the most appropriate adaptation plan among all possible plans. The third challenge is to resolve conflicting or overlapping semantic constraints, in particular conflicts arising from constraints expressed by owner's intellectual property rights about the modification of the content. In this thesis, we tackled the aforementioned challenges by proposing a Utility Function (UF), which integrates semantic concerns with user's perceptual considerations. This UF models the relationships among adaptation operations, user preferences, and the quality of the video content. We integrated this UF into an ADTE. This ADTE performs a multi-level piecewise reasoning to choose the adaptation plan that maximizes the user-perceived quality. Furthermore, we included intellectual property rights in the adaptation process. Thereby, we modeled content owner constraints. We dealt with the problem of conflicting user and owner constraints by mapping it to a known optimization problem. Moreover, we developed the SVCAT, which produces structural and high-level semantic annotation according to an original object-based video content model. We modeled as well the user's preferences proposing extensions to MPEG-7 and MPEG-21. All the developed contributions were carried out as part of a coherent framework called PIAF. PIAF is a complete modular MPEG standard compliant framework that covers the whole process of semantic video adaptation. We validated this research with qualitative and quantitative evaluations, which assess the performance and the efficiency of the proposed adaptation decision-taking engine within PIAF. The experimental results show that the proposed UF has a high correlation with subjective video quality evaluation.}, subject = {MPEG-Standard}, language = {en} } @phdthesis{MianSyed2003, author = {Mian Syed, Ahmed}, title = {Eine {\"o}konomische statische Analysemethode zur Berechnung von Relational Attributes mittels regul{\"a}rer Pfadbedingungen und ihre Anwendung auf Zeigeranalyse}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-333}, school = {Universit{\"a}t Passau}, year = {2003}, abstract = {Ziel der Arbeit ist es, eine neue Programmanalysetechnik f{\"u}r Zeigeranalyse zu entwickeln. Diese soll exakt in dem Sinne sein, daß sie nur Ergebnisse berechnet, die tats{\"a}chlich in realen Programml{\"a}ufen vorkommen k{\"o}nnen, Ebenso soll diese Analysetechnik {\"o}konomisch sein, d.h. nur den minimal f{\"u}r eine exakte L{\"o}sung ben{\"o}tigten Berechnungsaufwand investieren m{\"u}ssen.}, subject = {Softwareproduktion}, language = {de} } @phdthesis{Weitl2007, author = {Weitl, Franz}, title = {Document Verification with Temporal Description Logics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-12528}, school = {Universit{\"a}t Passau}, year = {2007}, abstract = {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.}, subject = {Verifikation}, language = {en} } @phdthesis{Schwaiger2008, author = {Schwaiger, Petra}, title = {Ein Bedingungsmodell f{\"u}r Planungsprobleme in strukturierten Dom{\"a}nen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-12497}, school = {Universit{\"a}t Passau}, year = {2008}, abstract = {Computerunterst{\"u}tzte 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 Flexibilit{\"a}t der Anfragen und der Vollst{\"a}ndigkeit und Korrektheit der Antworten hoch. Dies gilt insbesondere f{\"u}r Planungsprobleme in strukturierten Dom{\"a}nen. Derartige Probleme treten beispielsweise bei der Erstellung von Tests auf der Grundlage einer Menge von Fragen und gewissen Anforderungen an den Test, bei der Konsistenzpr{\"u}fung von Studienordnungen und bei der computerunterst{\"u}tzten Studienberatung auf. In der vorliegenden Arbeit wird ein Framework zur Behandlung eben genannter Probleme pr{\"a}sentiert. Die vorgestellte L{\"o}sung bietet durch den modellbasierten Ansatz und die entwickelte anwendungsnahe Modellierungssprache - gerade auch im Vergleich zu existierenden Ans{\"a}tzen - einen sehr hohen Grad an Abstraktion, Allgemeing{\"u}ltigkeit, Ausdrucksst{\"a}rke, Flexibilit{\"a}t 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 dar{\"u}ber hinaus als Formalisierung und Verallgemeinerung von Pfadconstraints bzw. Pfadanfragen in hierarchischen Datenmodellen aufgefasst werden. F{\"u}r die interne Repr{\"a}sentation erweist sich ein logikbasierter Ansatz mit Constraints, n{\"a}mlich Answer Set Programming mit Gewichten, als eine ausgezeichnete Methode bez{\"u}glich der Ausdrucksst{\"a}rke, M{\"a}chtigkeit und Ad{\"a}quatheit. Die Praxistauglichkeit des verfolgten Ansatzes im Hinblick auf Performanz und Skalierbarkeit wird in verschiedenen realen Anwendungsf{\"a}llen demonstriert.}, subject = {Logik}, language = {de} } @phdthesis{Graf2007, author = {Graf, Simone}, title = {Kamerakalibrierung mit radialer Verzeichnung - die radiale essentielle Matrix}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-12711}, school = {Universit{\"a}t Passau}, year = {2007}, abstract = {In der Bildverarbeitung wird die beobachtende Kamera meist als Lochkamera modelliert: ein Modell, das zahlreiche theoretische Vorteile bietet. So kann etwa das Abbildungsverhalten als projektive Abbildung aufgefasst werden. In einem Stereokamerasystem dieses Modells stehen korrespondierende Punkte - das sind Bildpunkte desselben 3D-Punktes - in einem linearen Zusammenhang, der auch ohne Kenntnis der Kameraparameter aus beobachteten Korrespondenzen gesch{\"a}tzt werden kann. F{\"u}r die meisten Kameras, insbesondere f{\"u}r solche mit Weitwinkelobjektiven, ist die Modellannahme einer Lochkamera allerdings sichtbar unzureichend. Deshalb m{\"u}ssen zus{\"a}tzlich zur Lochkamera noch Verzeichnungsabbildungen ins Modell integriert werden. In dieser Arbeit wird gezeigt, dass bei polynomialer radialer Verzeichnung die Parameter der Projektionsabbildung die Verzeichnungsparameter bestimmen. Dieses theoretische Ergebnis fließt in Algorithmen zur Kamerakalibrierung, d.h. zur Bestimmung der Parameter eines Kameramodells, ein. Diese wurden experimentell getestet und mit bestehenden Verfahren verglichen. Weiterhin wird die radiale essentielle Matrix eingef{\"u}hrt, die die Beziehung von korrespondierenden Punkten im Stereokamerafall bei radialer Verzeichnung beschreibt. Es werden vier Algorithmen vorgestellt, die diese theoretische Beziehung verwerten. Sie geben an, wie aus korrespondierenden Punkten die radiale essentielle Matrix gesch{\"a}tzt werden kann und welche Kameraparameter daraus gewonnen werden k{\"o}nnen. Damit ist beispielsweise eine Nachkalibrierung m{\"o}glich. Auch diese Verfahren wurden implementiert und evaluiert. Umgekehrt ist bei bekannter radialer essentieller Matrix eine Einschr{\"a}nkung des Suchraums f{\"u}r korrespondierende Punkte m{\"o}glich, die f{\"u}r die Rekonstruktion ben{\"o}tigt werden.}, subject = {Optische Messtechnik}, language = {de} } @unpublished{Kreitmeier2008, author = {Kreitmeier, Wolfgang}, title = {Optimal quantization for uniform distributions on Cantor-like sets}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-12449}, year = {2008}, abstract = {In this paper, the problem of optimal quantization is solved for uniform distributions on some higher dimensional, not necessarily self-similar \$N-\$adic Cantor-like sets. The optimal codebooks are determined and the optimal quantization error is calculated. The existence of the quantization dimension is characterized and it is shown that the quantization coefficient does not exist. The special case of self-similarity is also discussed. The conditions imposed are a separation property of the distribution and strict monotonicity of the first \$N\$ quantization error differences. Criteria for these conditions are proved and as special examples modified versions of classical fractal distributions are discussed.}, subject = {Maßtheorie}, language = {en} } @phdthesis{Guppenberger2010, author = {Guppenberger, Michael}, title = {Enhancing Information Systems with Event-Handling - A Non-Invasive Approach}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-22485}, school = {Universit{\"a}t Passau}, year = {2010}, abstract = {Due to the immense advance of widely accessible information systems in industrial applications, science, education and every day use, it becomes more and more difficult for users of those information systems to keep track with new and updated information. An approach to cope with this problem is to go beyond traditional search facilities and instead use the users' profiles to monitor data changes and to actively inform them about these updates - an aspect that has to be explicitly developed and integrated into a variety of information systems. This is traditionally done in an individual way, depending on the application and its platform. In this dissertation, we present a novel approach to model the semantic interrelations that specify which users to inform about which updates, based on the underlying model of the respective information system. For the first time, a meta-model that allows information system designers to tag an arbitrary data model and thus specify the event-handling semantics is presented. A formal specification of how to interpret meta-models to determine the receivers of the events completes the presented concept. For the practical realization of this new concept, model driven architecture (MDA) shows to be an ideal technical means. Using our newly developed UML profile based on data-modelling standards, an implementation of the event-handling specification can automatically be generated for a variety of different target platforms, like e.g. relational databases, using triggers. This meta-approach makes the proposed solution ideal with respect to maintainability and genericity. Our solution significantly reduces the overall development efforts for an event-handling facility. In addition, the enhanced model of the information system can be used to generate an implementation that also fulfils non-functional requirements like high performance and extensibility. The overall framework, consisting of the domain specific language (i.e. the meta-model), formal and technical transformations of how to interpret the enhanced information system model and a cost-based optimizing strategy, constitutes an integrated approach, offering several advantages over traditional implementation techniques: our framework can be applied to new information systems as well as to legacy applications without having to modify existing systems; it offers an extensible, easy-to-use, generic and thus re-usable solution and it can be tailored to and optimized for many use cases, as the practical evaluation presented in this dissertation verifies.}, subject = {Notifikation}, language = {en} } @phdthesis{Berl2011, author = {Berl, Andreas}, title = {Energy Efficiency in Office Computing Environments}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-22516}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {The increasing cost of energy and the worldwide desire to reduce CO2 emissions has raised concern about the energy efficiency of information and communication technology. Whilst research has focused on data centres recently, this thesis identifies office computing environments as significant consumers of energy. Office computing environments offer great potential for energy savings: On one hand, such environments consist of a large number of hosts. On the other hand, these hosts often remain turned on 24~hours per day while being underutilised or even idle. This thesis analyzes the energy consumption within office computing environments and suggests an energy-efficient virtualized office environment. The office environment is virtualized to achieve flexible virtualized office resources that enable an energy-based resource management. This resource management stops idle services and idle hosts from consuming resources within the office and consolidates utilised office services on office hosts. This increases the utilisation of some hosts while other hosts are turned off to save energy. The suggested architecture is based on a decentralized approach that can be applied to all kinds of office computing environments, even if no centralized data centre infrastructure is available. The thesis develops the architecture of the virtualized office environment together with an energy consumption model that is able to estimate the energy consumption of hosts and network within office environments. The model enables the energy-related comparison of ordinary and virtualized office environments, considering the energy-efficient management of services. Furthermore, this thesis evaluates energy efficiency and overhead of the suggested approach. First, it theoretically proves the energy efficiency of the virtualized office environment with respect to the energy consumption model. Second, it uses Markov processes to evaluate the impact of user behaviour on the suggested architecture. Finally, the thesis develops a discrete-event simulation that enables the simulation and evaluation of office computing environments with respect to varying virtualization approaches, resource management parameters, user behaviour, and office equipment. The evaluation shows that the virtualized office environment saves more than half of the energy consumption within office computing environments, depending on user behaviour and office equipment.}, subject = {Energieeffizienz}, language = {en} } @unpublished{Kreitmeier2011, author = {Kreitmeier, Wolfgang}, title = {Optimal vector quantization in terms of Wasserstein distance}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-22502}, year = {2011}, abstract = {The optimal quantizer in memory-size constrained vector quantization induces a quantization error which is equal to a Wasserstein distortion. However, for the optimal (Shannon-)entropy constrained quantization error a proof for a similar identity is still missing. Relying on principal results of the optimal mass transportation theory, we will prove that the optimal quantization error is equal to a Wasserstein distance. Since we will state the quantization problem in a very general setting, our approach includes the R\'enyi-\$\alpha\$-entropy as a complexity constraint, which includes the special case of (Shannon-)entropy constrained \$(\alpha = 1)\$ and memory-size constrained \$(\alpha = 0)\$ quantization. Additionally, we will derive for certain distance functions codecell convexity for quantizers with a finite codebook. Using other methods, this regularity in codecell geometry has already been proved earlier by Gy\"{o}rgy and Linder.}, subject = {Maßtheorie}, language = {en} } @phdthesis{Stoerzer2006, author = {St{\"o}rzer, Maximilian}, title = {Impact Analysis for AspectJ - A Critical Analysis and Tool-Based Approach to AOP}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-897}, school = {Universit{\"a}t Passau}, year = {2006}, abstract = {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.}, subject = {Modularit{\"a}t}, language = {en} } @phdthesis{Kickingereder2006, author = {Kickingereder, Reiner}, title = {Optische Vermessung partiell reflektierender Oberfl{\"a}chen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-936}, school = {Universit{\"a}t Passau}, year = {2006}, abstract = {Die vorliegende Arbeit befaßt sich mit der dreidimensionalen Rekonstruktion reflektierender Oberfl{\"a}chen. Dabei wird sowohl die Oberfl{\"a}chenform als auch die absolute Lage im Raum bestimmt. Es werden Oberfl{\"a}chen behandelt, die einerseits total reflektieren, andererseits diffuse und spiegelnde Reflexionsanteile aufweisen. Zur L{\"o}sung des Problems werden zwei Kameras und mehrere Lichtquellen verwendet. Eine genauere Analyse der Lichtreflexion an spiegelnden Objekten f{\"u}hrt zu einer Beschreibung des Problems als L{\"o}sung einer totalen Differentialgleichung. Diese L{\"o}sung wird als Startwert f{\"u}r die Rekonstruktion partiell reflektierender Oberfl{\"a}chen verwendet.}, subject = {Dreidimensionale Rekonstruktion}, language = {de} } @unpublished{Kreitmeier2005, author = {Kreitmeier, Wolfgang}, title = {Optimal Quantization for Dyadic Homogeneous Cantor Distributions}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-3845}, year = {2005}, abstract = {For a large class of dyadic homogeneous Cantor distributions in \mathbb{R}, which are not necessarily self-similar, we determine the optimal quantizers, give a characterization for the existence of the quantization dimension, and show the non-existence of the quantization coefficient. The class contains all self-similar dyadic Cantor distributions, with contraction factor less than or equal to \frac{1}{3}. For these distributions we calculate the quantization errors explicitly.}, subject = {Maßtheorie}, language = {en} } @phdthesis{Hoelbling2011, author = {H{\"o}lbling, G{\"u}nther}, title = {Personalized Means of Interacting with Multimedia Content}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-24210}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {Today the world of multimedia is almost completely device- and content-centered. It focuses it's energy nearly exclusively on technical issues such as computing power, network specifics or content and device characteristics and capabilities. In most multimedia systems, the presentation of multimedia content and the basic controls for playback are main issues. Because of this, a very passive user experience, comparable to that of traditional TV, is most often provided. In the face of recent developments and changes in the realm of multimedia and mass media, this "traditional" focus seems outdated. The increasing use of multimedia content on mobile devices, along with the continuous growth in the amount and variety of content available, make necessary an urgent re-orientation of this domain. In order to highlight the depth of the increasingly difficult situation faced by users of such systems, it is only logical that these individuals be brought to the center of attention. In this thesis we consider these trends and developments by applying concepts and mechanisms to multimedia systems that were first introduced in the domain of usercentrism. Central to the concept of user-centrism is that devices should provide users with an easy way to access services and applications. Thus, the current challenge is to combine mobility, additional services and easy access in a single and user-centric approach. This thesis presents a framework for introducing and supporting several of the key concepts of user-centrism in multimedia systems. Additionally, a new definition of a user-centric multimedia framework has been developed and implemented. To satisfy the user's need for mobility and flexibility, our framework makes possible seamless media and service consumption. The main aim of session mobility is to help people cope with the increasing number of different devices in use. Using a mobile agent system, multimedia sessions can be transferred between different devices in a context-sensitive way. The use of the international standard MPEG-21 guarantees extensibility and the integration of content adaptation mechanisms. Furthermore, a concept is presented that will allow for individualized and personalized selection and face the need for finding appropriate content. All of which can be done, using this approach, in an easy and intuitive way. Especially in the realm of television, the demand that such systems cater to the need of the audience is constantly growing. Our approach combines content-filtering methods, state-of-the-art classification techniques and mechanisms well known from the area of information retrieval and text mining. These are all utilized for the generation of recommendations in a promising new way. Additionally, concepts from the area of collaborative tagging systems are also used. An extensive experimental evaluation resulted in several interesting findings and proves the applicability of our approach. In contrast to the "lean-back" experience of traditional media consumption, interactive media services offer a solution to make possible the active participation of the audience. Thus, we present a concept which enables the use of interactive media services on mobile devices in a personalized way. Finally, a use case for enriching TV with additional content and services demonstrates the feasibility of this concept.}, subject = {Empfehlungssystem}, language = {en} } @phdthesis{Johns2009, author = {Johns, Martin}, title = {Code Injection Vulnerabilities in Web Applications - Exemplified at Cross-site Scripting}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-23626}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {The majority of all security problems in today's Web applications is caused by string-based code injection, with Cross-site Scripting (XSS)being the dominant representative of this vulnerability class. This thesis discusses XSS and suggests defense mechanisms. We do so in three stages: First, we conduct a thorough analysis of JavaScript's capabilities and explain how these capabilities are utilized in XSS attacks. We subsequently design a systematic, hierarchical classification of XSS payloads. In addition, we present a comprehensive survey of publicly documented XSS payloads which is structured according to our proposed classification scheme. Secondly, we explore defensive mechanisms which dynamically prevent the execution of some payload types without eliminating the actual vulnerability. More specifically, we discuss the design and implementation of countermeasures against the XSS payloads Session Hijacking'', Cross-site Request Forgery'', and attacks that target intranet resources. We build upon this and introduce a general methodology for developing such countermeasures: We determine a necessary set of basic capabilities an adversary needs for successfully executing an attack through an analysis of the targeted payload type. The resulting countermeasure relies on revoking one of these capabilities, which in turn renders the payload infeasible. Finally, we present two language-based approaches that prevent XSS and related vulnerabilities: We identify the implicit mixing of data and code during string-based syntax assembly as the root cause of string-based code injection attacks. Consequently, we explore data/code separation in web applications. For this purpose, we propose a novel methodology for token-level data/code partitioning of a computer language's syntactical elements. This forms the basis for our two distinct techniques: For one, we present an approach to detect data/code confusion on run-time and demonstrate how this can be used for attack prevention. Furthermore, we show how vulnerabilities can be avoided through altering the underlying programming language. We introduce a dedicated datatype for syntax assembly instead of using string datatypes themselves for this purpose. We develop a formal, type-theoretical model of the proposed datatype and proof that it provides reliable separation between data and code hence, preventing code injection vulnerabilities. We verify our approach's applicability utilizing a practical implementation for the J2EE application server.}, subject = {Computersicherheit}, language = {en} } @phdthesis{Rabl2011, author = {Rabl, Tilmann}, title = {Efficiency in Cluster Database Systems - Dynamic and Workload-Aware Scaling and Allocation}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-25821}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {Database systems have been vital in all forms of data processing for a long time. In recent years, the amount of processed data has been growing dramatically, even in small projects. Nevertheless, database management systems tend to be static in terms of size and performance which makes scaling a difficult and expensive task. Because of performance and especially cost advantages more and more installed systems have a shared nothing cluster architecture. Due to the massive parallelism of the hardware programming paradigms from high performance computing are translated into data processing. Database research struggles to keep up with this trend. A key feature of traditional database systems is to provide transparent access to the stored data. This introduces data dependencies and increases system complexity and inter process communication. Therefore, many developers are exchanging this feature for a better scalability. However, explicitly managing the data distribution and data flow requires a deep understanding of the distributed system and reduces the possibilities for automatic and autonomic optimization. In this thesis we present an approach for database system scaling and allocation that features good scalability although it keeps the data distribution transparent. The first part of this thesis analyzes the challenges and opportunities for self-scaling database management systems in cluster environments. Scalability is a major concern of Internet based applications. Access peaks that overload the application are a financial risk. Therefore, systems are usually configured to be able to process peaks at any given moment. As a result, server systems often have a very low utilization. In distributed systems the efficiency can be increased by adapting the number of nodes to the current workload. We propose a processing model and an architecture that allows efficient self-scaling of cluster database systems. In the second part we consider different allocation approaches. To increase the efficiency we present a workload-aware, query-centric model. The approach is formalized; optimal and heuristic algorithms are presented. The algorithms optimize the data distribution for local query execution and balance the workload according to the query history. We present different query classification schemes for different forms of partitioning. The approach is evaluated for OLTP and OLAP style workloads. It is shown that variants of the approach scale well for both fields of application. The third part of the thesis considers benchmarks for large, adaptive systems. First, we present a data generator for cloud-sized applications. Due to its architecture the data generator can easily be extended and configured. A key feature is the high degree of parallelism that makes linear speedup for arbitrary numbers of nodes possible. To simulate systems with user interaction, we have analyzed a productive online e-learning management system. Based on our findings, we present a model for workload generation that considers the temporal dependency of user interaction.}, subject = {Verteiltes Datenbanksystem}, language = {en} } @phdthesis{Ali2011, author = {Ali, Rashid}, title = {Weyl Gr{\"o}bner Basis Cryptosystems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-23195}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {In this thesis, we shall consider a certain class of algebraic cryptosystems called Gr{\"o}bner Basis Cryptosystems. In 1994, Koblitz introduced the Polly Cracker cryptosystem that is based on the theory of Gr{\"o}bner basis in commutative polynomials rings. The security of this cryptosystem relies on the fact that the computation of Gr{\"o}bner basis is, in general, EXPSPACE-hard. Cryptanalysis of these commutative Polly Cracker type cryptosystems is possible by using attacks that do not require the computation of Gr{\"o}bner basis for breaking the system, for example, the attacks based on linear algebra. To secure these (commutative) Gr{\"o}bner basis cryptosystems against various attacks, among others, Ackermann and Kreuzer introduced a general class of Gr{\"o}bner Basis Cryptosystems that are based on the difficulty of computing module Gr{\"o}bner bases over general non-commutative rings. The objective of this research is to describe a special class of such cryptosystems by introducing the Weyl Gr{\"o}bner Basis Cryptosystems. We divide this class of cryptosystems in two parts namely the (left) Weyl Gr{\"o}bner Basis Cryptosystems and Two-Sided Weyl Gr{\"o}bner Basis Cryptosystems. We suggest to use Gr{\"o}bner bases for left and two-sided ideals in Weyl algebras to construct specific instances of such cryptosystems. We analyse the resistance of these cryptosystems to the standard attacks and provide computational evidence that secure Weyl Gr{\"o}bner Basis Cryptosystems can be built using left (resp. two-sided) Gr{\"o}bner bases in Weyl algebras.}, subject = {Gr{\"o}bner-Basis}, language = {en} } @unpublished{KreitmeierLinder2011, author = {Kreitmeier, Wolfgang and Linder, Tamas}, title = {High-Resolution Scalar Quantization with R{\´e}nyi Entropy Constraint}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-23787}, year = {2011}, abstract = {We consider optimal scalar quantization with \$r\$th power distortion and constrained R\'enyi entropy of order \$\alpha\$. For sources with absolutely continuous distributions the high rate asymptotics of the quantizer distortion has long been known for \$\alpha=0\$ (fixed-rate quantization) and \$\alpha=1\$ (entropy-constrained quantization). These results have recently been extended to quantization with R\'enyi entropy constraint of order \$\alpha \ge r+1\$. Here we consider the more challenging case \$\alpha\in [-\infty,0)\cup (0,1)\$ and for a large class of absolutely continuous source distributions we determine the sharp asymptotics of the optimal quantization distortion. The achievability proof is based on finding (asymptotically) optimal quantizers via the companding approach, and is thus constructive.}, subject = {Maßtheorie}, language = {de} } @phdthesis{Houyou2009, author = {Houyou, Amine Mohamed}, title = {Context-Aware Mobility: A Distributed Approach to Context Management}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-17975}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {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.}, subject = {Netze}, language = {en} } @phdthesis{Ogris2009, author = {Ogris, Georg}, title = {Multi-modal on-body sensing of human activities}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-17930}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {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.}, subject = {Kontextbezogenes System}, language = {de} } @unpublished{Kreitmeier2009, author = {Kreitmeier, Wolfgang}, title = {Hausdorff measure of uniform self-similar fractals}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-17948}, year = {2009}, abstract = {Let d \&\#8805; 1 be an integer and E a self-similar fractal set, which is the attractor of a uniform contracting iterated function system (UIFS) on Rd. Denote by D the Hausdorff dimension, by HD(E) the Hausdorff measure and by diam (E) the diameter of E. If the UIFS is parametrised by its contracting factor c, while the set \ω of fixed points of the UIFS does not depend on c, we will show the existence of a positive constant depending only on \ω, such that the Hausdorff dimension is smaller than one and HD = (E) D if c is smaller than this constant. We apply our result to modified versions of various classical fractals. Moreover we present a parametrised UIFS where \ω depends on c and HD < diam(E)D, if c is small enough.}, subject = {Maßtheorie}, language = {en} } @unpublished{Kreitmeier2009, author = {Kreitmeier, Wolfgang}, title = {Optimal quantization for the one-dimensional uniform distribution with R{\´e}nyi -α-entropy constraints}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-16983}, year = {2009}, abstract = {We establish the optimal quantization problem for probabilities under constrained R{\´e}nyi-α-entropy of the quantizers. We determine the optimal quantizers and the optimal quantization error of one-dimensional uniform distributions including the known special cases α = 0 (restricted codebook size) and α = 1 (restricted Shannon entropy).}, subject = {Maßtheorie}, language = {de} } @phdthesis{Oberender2009, author = {Oberender, Jens O.}, title = {Widerstandsf{\"a}hige Anonymisierungsnetze}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-16846}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {Unverkettbare Nachrichten sind ein Grundbaustein anonymer Kommunikation. Anonymisierungsnetze sch{\"u}tzen mittels Unverkettbarkeit, wer mit wem kommuniziert sowie die Identit{\"a}t der Beteiligten einer Kommunikationsbeziehung. Anonymisierungsnetze ben{\"o}tigen Kooperation, da die Anonymit{\"a}t durch Ressourcen anderer Teilnehmer gesch{\"u}tzt 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 Widerstandsf{\"a}higkeit dieser Netze beeintr{\"a}chtigt. St{\"o}rungen werden in einem spieltheoretischen Modell untersucht, um widerstandsf{\"a}hige Konfigurationen von Anonymisierungsnetzen zu ermitteln. Eine weitere St{\"o}rquelle sind {\"U}berflutungsangriffe mittels unverkettbarer Nachrichten. Es soll sowohl die Verf{\"u}gbarkeit als auch die Anonymit{\"a}t gesch{\"u}tzt werden. Dazu wird Unverkettbarkeit f{\"u}r Nachrichten aufrecht erhalten, außer wenn die Senderate eines Nachrichtenstroms eine Richtlinie {\"u}berschreitet. Innerhalb verkettbarer Nachrichten k{\"o}nnen {\"U}berflutungsangriffe erkannt werden. Dar{\"u}ber kann die Verf{\"u}gbarkeit des Netzdienstes gesch{\"u}tzt werden.}, subject = {Anonymit{\"a}t}, language = {de} } @unpublished{Kreitmeier2009, author = {Kreitmeier, Wolfgang}, title = {Error bounds for high-resolution quantization with R{\´e}nyi - \&\#945; - entropy constraints}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-16647}, year = {2009}, abstract = {We consider the problem of optimal quantization with norm exponent r > 0 for Borel probabilities on Rd under constrained R{\´e}nyi-\&\#945;-entropy of the quantizers. If the bound on the entropy becomes large, then sharp asymptotics for the optimal quantization error are well-known in the special cases \&\#945; = 0 (memory-constrained quantization) and \&\#945; = 1 (Shannon-entropy-constrained quantization). In this paper we determine sharp asymptotics for the optimal quantization error under large entropy bound with entropy parameter \&\#945; \&\#8712; [1+r/d, \&\#8734;]. For \&\#945; \&\#8712; [0,1+r/d[ we specify the asymptotical order of the optimal quantization error under large entropy bound. The optimal quantization error decays exponentially fast with the entropy bound and the exact decay rate is determined for all \&\#945; \&\#8712; [0, \&\#8734;].}, subject = {Maßtheorie}, language = {en} } @phdthesis{Maydl2005, author = {Maydl, Walter}, title = {Komponentenbasierte Softwareentwicklung f{\"u}r datenflußorientierte eingebettete Systeme}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-681}, school = {Universit{\"a}t Passau}, year = {2005}, abstract = {Diese Dissertation besch{\"a}ftigt sich mit den Problemen bei der Entwicklung von effizienter und zuverl{\"a}ssiger Software f{\"u}r eingebettete Systeme. Eingebettete Systeme sind inh{\"a}rent nebenl{\"a}ufig, was mit einen Grund f{\"u}r ihre hohe Entwurfskomplexit{\"a}t darstellt. Aus dieser Nebenl{\"a}ufigkeit resultiert ein hoher Grad an Kommunikation zwischen den einzelnen Komponenten. Eine wichtige Forderung zur Vereinfachung des Entwurfsprozesses besteht in der getrennten Modellierung von Kommunikationsprotokollen und eigentlichen Verarbeitungsalgorithmen. Daraus resultiert eine h{\"o}here Wiederverwendbarkeit bei sich {\"a}ndernden Kommunikationsstrukturen. Die Grundlage f{\"u}r die sogenannten Datenflußsprachen bildet eine einfache von Gilles Kahn konzipierte Sprache f{\"u}r Parallelverarbeitung. In dieser Sprache besteht ein System aus einer Menge sequentieller Prozesse (Komponenten), die {\"u}ber Fifokan{\"a}le miteinander kommunizieren. Ein Prozess ist rechenbereit, wenn seine Eingangsfifos mit entsprechenden Daten gef{\"u}llt sind. {\"U}bertragen werden physikalische Signale, die als Str{\"o}me bezeichnet werden. Str{\"o}me sind Folgen von Werten ohne explizite Zeitangaben. Das Einsatzgebiet von Datenflußsprachen liegt in der Entwicklung von Programmen zur Bild- und Signalverarbeitung, typischen Aufgaben in eingebetteten Systemen. Die Programmierung erfolgt visuell, wobei man Icons als Repr{\"a}sentanten parametrisierbarer Komponenten aus einer Bibliothek ausw{\"a}hlt und mittels Kanten (Fifos) verbindet. Ein im allgemeinen dynamischer Scheduler {\"u}berwacht die Ausf{\"u}hrung des fertiggestellten Anwendungsprogramms. Diese Arbeit schl{\"a}gt ein universelleres Modell physikalischer Signale vor. Dabei werden zwei Ziele verfolgt: 1. Effiziente Kommunikation zwischen den Komponenten 2. Entwurfsbegleitende {\"U}berpr{\"u}fung von Programmeigenschaften unter Verwendung komplexerer Komponentenmodelle Zur Effizienzsteigerung werden nur relevante Werte innerhalb von Str{\"o}men {\"u}bertragen. Dies erh{\"o}ht zwar den Mehraufwand zur Kennzeichnung des Aufbaus eines Teilstroms, in praktischen Anwendungen ist die hier vorgestellte Methode jedoch effizienter. Die Einf{\"u}hrung neuer Signalmerkmale erlaubt unterschiedlichste {\"U}berpr{\"u}fungen der Einhaltung von Typregeln durch die Eingangs- und Ausgangsstr{\"o}me einer Komponente. Anstelle einfacher Schaltregeln werden aufwendigere Kommunikationsprotokolle f{\"u}r die verschiedenen Arten von Komponenten eingef{\"u}hrt. Fifomaten (Fifo-Automaten) dienen als formale Grundlage. Mittels eines dezidierten Model-Checking-Verfahrens wird das Zusammenspiel der Fifomaten daraufhin untersucht, ob ein zyklischer Schedule existiert. Die Existenz eines solchen zyklischen Schedules schließt Speicher{\"u}berlauf und Deadlocks aus und garantiert dar{\"u}ber hinaus, daß das Programm nach endlicher Zeit wieder in die Ausgangssituation zur{\"u}ckfindet. Da im allgemeinen die Datenflußprogramme turing{\"a}quivalent sind, kann es allerdings zyklische Schedules geben, die das Verfahren nicht entdeckt. Mit der hier vorgestellten und implementierten Methode wird die Entwicklungszeit korrekter Datenflußprogramme deutlich reduziert. Das neue Modell physikalischer Signale macht zudem die Ausf{\"u}hrung effizienter.}, subject = {Softwareentwicklung}, language = {de} } @phdthesis{Schwarzfischer2004, author = {Schwarzfischer, Thomas}, title = {Quality and Utility - On the Use of Time-Value Functions to Integrate Quality and Timeliness Flexible Aspects in a Dynamic Real-Time Scheduling Environment}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-619}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {Scheduling methodologies for real-time applications have been of keen interest to diverse research communities for several decades. Depending on the application area, algorithms have been developed that are tailored to specific requirements with respect to both the individual components of which an application is made up and the computational platform on which it is to be executed. Many real-time scheduling algorithms base their decisions solely or partly on timing constraints expressed by deadlines which must be met even under worst-case conditions. The increasing complexity of computing hardware means that worst-case execution time analysis becomes increasingly pessimistic. Scheduling hard real-time computations according to their worst-case execution times (which is common practice) will thus result, on average, in an increasing amount of spare capacity. The main goal of flexible real-time scheduling is to exploit this otherwise wasted capacity. Flexible scheduling schemes have been proposed to increase the ability of a real-time system to adapt to changing requirements and nondeterminism in the application behaviour. These models can be categorised as those whose source of flexibility is the quality of computations and those which are flexible regarding their timing constraints. This work describes a novel model which allows to specify both flexible timing constraints and quality profiles for an application. Furthermore, it demonstrates the applicability of this specification method to real-world examples and suggests a set of feasible scheduling algorithms for the proposed problem class.}, subject = {Echtzeitsystem}, language = {en} } @phdthesis{Kreitmeier2006, author = {Kreitmeier, Wolfgang}, title = {Optimale Quantisierung verallgemeinerter Cantor-Verteilungen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-913}, school = {Universit{\"a}t Passau}, year = {2006}, abstract = {F{\"u}r verallgemeinerte Cantor-Verteilungen, die im Eindimensionalen mittels klassischer Wischkonstruktion bzw. in h{\"o}heren Dimensionen {\"u}ber iterierte Funktionensysteme definiert werden, wird das Problem der optimalen Quantisierung unter bestimmten Voraussetzungen vollst{\"a}ndig gel{\"o}st. Es werden die optimalen Codeb{\"u}cher bestimmt und Formeln f{\"u}r den optimalen Quantisierungsfehler bewiesen. Im eindimensionalen Fall wird eine Existenzcharakterisierung der Quantisierungsdimension gegeben und unter bestimmten Voraussetzungen die Nichtexistenz des Quantisierungskoeffizienten gezeigt. Auch in h{\"o}heren Dimensionen wird f{\"u}r die betrachteten Verteilungen bewiesen, dass der Quantisierungskoeffizient, bei existenter Quantisierungsdimension, nicht existiert. Die gewonnenen Resultate werden auf die Gleichverteilungen von modifizierten klassischen fraktalen Mengen, wie das Sierpinski-Dreieck, die Cantormenge und den Cantor-Staub angewandt.}, subject = {Maßtheorie}, language = {de} } @unpublished{Kreitmeier2007, author = {Kreitmeier, Wolfgang}, title = {Optimal quantization of probabilities concentrated on small balls}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-12010}, year = {2007}, abstract = {We consider probability distributions which are uniformly distributed on a disjoint union of balls with equal radius. For small enough radius the optimal quantization error is calculated explicitly in terms of the ball centroids. We apply the results to special self-similar measures.}, subject = {Maßtheorie}, language = {en} } @unpublished{Kreitmeier2007, author = {Kreitmeier, Wolfgang}, title = {Asymptotic order of quantization for Cantor distributions in terms of Euler characteristic, Hausdorff and Packing measure}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-7374}, year = {2007}, abstract = {For homogeneous one-dimensional Cantor sets, which are not necessarily self-similar, we show under some restrictions that the Euler exponent equals the quantization dimension of the uniform distribution on these Cantor sets. Moreover for a special sub-class of these sets we present a linkage between the Hausdorff and the Packing measure of these sets and the high-rate asymptotics of the quantization error.}, subject = {Maßtheorie}, language = {en} } @phdthesis{Ramsauer2005, author = {Ramsauer, Markus}, title = {Energie- und qualit{\"a}tsbewußte Einplanung von periodischen Prozessen in eingebetteten Echtzeitsystemen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-628}, school = {Universit{\"a}t Passau}, year = {2005}, abstract = {Mobile Ger{\"a}te dienen immer h{\"a}ufiger zur Ausf{\"u}hrung von Echtzeitanwendungen, sie bieten immer mehr Rechenleistung und sie werden kleiner und leichter. Hohe Rechenleistung erfordert jedoch sehr viel Energie, was im Gegensatz zu den geringen Akkukapazit{\"a}ten, die aus der Forderung nach kleinen und leichten Ger{\"a}ten resultieren, steht. Bei der Echtzeiteinplanung von Rechenprozessen gewinnt daher der Energieverbrauch der Ger{\"a}te neben der rechtzeitigen Beendigung von Anwendungen zunehmend an Bedeutung, weil sie m{\"o}glichst lange unabh{\"a}ngig vom Stromnetz betrieben werden sollen. Andererseits werden auf diesen Ger{\"a}ten rechenintensive Anwendungen ausgef{\"u}hrt, bei denen es w{\"u}nschenswert ist, die maximale mit der verf{\"u}gbaren Rechenleistung erzielbare Qualit{\"a}t zu erhalten. In dieser Arbeit wird ein Systemmodell vorgestellt, das den Design-to-time-Ansatz mit den M{\"o}glichkeiten der dynamischen Leistungsanpassung (Rechenleistung und verbrauchte elektrische Leistung) moderner Prozessoren vereinigt. Der Design-to-time-Ansatz erm{\"o}glicht Energieeinsparungen oder Qualit{\"a}tssteigerungen durch die dynamische Auswahl alternativer Implementierungen, welche dieselbe Aufgabe mit unterschiedlicher Ausf{\"u}hrungsdauer und Qualit{\"a}t bzw. Energieverbrauch erf{\"u}llen. Das Systemmodell umfaßt unter anderem periodische Prozesse mit harten Echtzeitbedingungen, Datenabh{\"a}ngigkeiten und alternativen Implementierungen, sowie Prozessoren mit diskreten Leistungsstufen. Die Einplanung der Prozesse erfolgt in zwei Phasen. In der Offline-Phase wird ein flexibler Schedule berechnet, der f{\"u}r die zur Laufzeit m{\"o}glichen Kombinationen von verstrichener Zeit und noch einzuplanender Prozeßmenge den jeweils einzuplanenden Prozeß, sowie die zu verwendende Implementierung und gegebenenfalls die einzustellende Leistungsstufe beinhaltet. Dieser flexible Schedule wird w{\"a}hrend der Online-Phase mit vernachl{\"a}ssigbarem Zeit- und Energieaufwand von einem Scheduler interpretiert. F{\"u}r die Berechnung der optimalen flexiblen Schedules wurde ein Optimierer entwickelt, der eine Folge von flexiblen Schedules mit monoton steigender G{\"u}te (niedriger Energieverbrauch bzw. hohe Qualit{\"a}t) generiert, und damit der Klasse der Anytime-Algorithmen zuzuordnen ist. Eine Variante der Dynamischen Programmierung dient zur Bestimmung global optimaler, flexibler Schedules, die beispielsweise als Basis f{\"u}r Benchmarks dienen. Eine auf Simulated Annealing basierende Variante des Optimierers erm{\"o}glicht ein schnelleres Auffinden guter, flexibler Schedules f{\"u}r umfangreichere Anwendungen.}, subject = {Echtzeitsystem}, language = {de} } @phdthesis{Raitner2005, author = {Raitner, Marcus}, title = {Efficient visual navigation of hierarchically structured graphs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-658}, school = {Universit{\"a}t Passau}, year = {2005}, abstract = {Visual navigation of hierarchically structured graphs is a technique for interactively exploring large graphs that possess an additional hierarchical structure. This structure is expressed in form of a recursive clustering of the nodes: in call graphs of telephone networks, for instance, the nodes are identified with phone numbers; they are clustered recursively through the implicit structure of the numbers, e. g., nodes with the same area code belong to a cluster. In order to reduce the complexity and the size of the graph, only those subgraphs that are currently needed are shown in detail, while the others are collapsed, i. e., represented by meta nodes. In such a graph view the subgraphs in the areas of interest are expanded furthest, whereas those on the periphery are abstracted. As the areas of interest change over time, clusters in a view need to be expanded or contracted. First and foremost, there is need for an efficient data structure for this graph view maintenance problem. Depending on the admissible modifications of the graph and its hierarchical clustering, three variants have been discussed in the literature: in the static case, everything is fixed; in the dynamic graph variant, only edges of the graph can be inserted and deleted; finally, in the dynamic graph and tree variant the graph additionally is subject to node insertions and deletions and the clustering may change through splitting and merging of clusters. We introduce a new variant, dynamic leaves, which is based on the dynamic graph variant, but additionally allows insertion and deletion of graph nodes, i. e., leaves of the hierarchy. So far efficient data structures were known only for the static and the dynamic graph variant, i. e., neither the nodes of the graph nor the clustering could be modified. As this is unsatisfactory in an interactive editor for hierarchically structured graphs, we first generalize the approach of Buchsbaum et. al (Proc. 8th ESA, vol. 1879 of LNCS, pp. 120-131, 2000), in which graph view maintenance is formulated as a special case of range searching over tree cross products, to the new dynamic leaves variant. This generalization builds on a novel technique of superimposing a search tree over an ordered list maintenance structure. With an additional factor of roughly O(log n/log log n), this is the first data structure for the problem of graph view maintenance where the node set is dynamic. Visualizing the expanding and contracting appropriately is the second challenge. We propose a local update scheme for the algorithm of Sugiyama and Misue (IEEE Trans. on Systems, Man, and Cybernetics 21 (1991) 876- 892) for drawing compound digraphs. The layered drawings that it produces have many applications ranging from biochemical pathways to UML diagrams. Modifying the intermediate results of every step of the original algorithm locally, the update scheme is more efficient than re-applying the entire algorithm after expansion or contraction. As our experimental results on randomly generated graphs show, the average time for updating the drawing is around 50 \% of the time for redrawing for dense graphs and below 20 \% for sparse graphs. Also, the performance gain is not at the expense of quality as regards the area of the drawing, which increases only insignificantly, and the number of crossings, which is reduced. At the same time, the locality of the updates preserves the user 's mental map of the graph: nodes that are are not affected stay on the same level in the same relative order and expanded edges take the same course as the corresponding contracted edge; furthermore, expansion and contraction are visually inverse. Finally, our new data structure and the update scheme are combined into an interactive editor and viewer for compound (di-)graphs. A flexible and extensible software architecture is introduced that lays the ground for future research. It employs the well-known Model-View-Controller (MVC) paradigm to separate the abstract data from its presentation. As a consequence, the purely combinatorial parts, i. e., the compound (di-)graph and its views, are reusable without the editor front-end. A proof-of-concept implementation based on the proposed architecture shows its feasibility and suitability.}, subject = {Dynamische Datenstruktur}, language = {en} } @phdthesis{Lauren2005, author = {Lauren, Verena}, title = {Semilineare Approximation in der Bildrekonstruktion}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-730}, school = {Universit{\"a}t Passau}, year = {2005}, abstract = {In der Bildverarbeitung spielen Segmentierungsalgorithmen, bei denen die Art der zu segmentierenden Menge schon im Voraus festgelegt werden kann und nur noch ihre Gr{\"o}ße und Lage angepasst werden muss, eine eher untergeordnete Rolle. Gr{\"u}nde hierf{\"u}r sind vor allem komplizierte Zielfunktionen und daraus resultierende lange Rechenzeiten, die zudem meist kein optimales Ergebnis liefern. Dabei kann eine mengenbasierte Segmentierung durchaus sinnvoll eingesetzt werden, wenn gewisse Rahmenbedingungen eingehalten werden. In dieser Arbeit wird eine Theorie zur allgemeinen mengenbasierten Segmentierung vorgestellt und untersucht, unter welchen Bedingungen optimale Segmentierungsergebnisse erreicht werden k{\"o}nnen. Die anschließenden Anwendungen best{\"a}tigen die N{\"u}tzlichkeit dieser Theorie.}, subject = {Optimale Rekonstruktion}, language = {de} } @phdthesis{Streckenbach2005, author = {Streckenbach, Mirko}, title = {KABA - a system for refactoring Java programs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-638}, school = {Universit{\"a}t Passau}, year = {2005}, abstract = {Refactoring is a well known technique to enhance various aspects of an object-oriented program. It has become very popular during recent years, as it allows to overcome deficits present in many programs. Doing refactoring by hand is almost impossible due to the size and complexity of modern software systems. Automated tools provide support for the application of refactorings, but do not give hints, which refactorings to apply and why. The Snelting/Tip analysis is a program analysis, which creates a refactoring proposal for a class hierarchy by analyzing how class members are used inside a program. KABA is an adaption and extension of the Snelting/Tip analysis for Java. It has been implemented and expanded to become a semantic preserving, interactive refactoring system. Case studies of real world programs will show the usefulness of the system and its practical value.}, subject = {Java }, language = {en} } @phdthesis{Fischer2005, author = {Fischer, Andreas}, title = {Peano-differentiable functions in O-Minimal structures}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-673}, school = {Universit{\"a}t Passau}, year = {2005}, abstract = {We discuss several aspects of Peano-differentiable functions which are definable in an o-minimal structure expanding a real closed field. After recalling some already known results about o-minimal structures we develop techniques for the intrinsic study of differentiable functions in these structures. After this we study (ordinary) differentiable functions definable in an o-minimal structure and their continuiuty properties along curves of different differentiability classes. Then we generalise (ordinary) differentiability to Peano-differentiability. We study differentiability of certain Peano-derivatives of definable functions and characterise the sets of non-continuity of these derivatives. In the end we study extendability of these functions defined on closed sets and give sufficient conditions by which we can extend functions as Peano-differentiable functions.}, subject = {Semialgebraische Menge}, language = {en} } @phdthesis{Wuechner2013, author = {W{\"u}chner, Patrick}, title = {Energy-Efficient and Timely Event Reporting Using Wireless Sensor Networks}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-27159}, school = {Universit{\"a}t Passau}, year = {2013}, abstract = {This thesis investigates the suitability of state-of-the-art protocols for large-scale and long-term environmental event monitoring using wireless sensor networks based on the application scenario of early forest fire detection. By suitable combination of energy-efficient protocol mechanisms a novel communication protocol, referred to as cross-layer message-merging protocol (XLMMP), is developed. Qualitative and quantitative protocol analyses are carried out to confirm that XLMMP is particularly suitable for this application area. The quantitative analysis is mainly based on finite-source retrial queues with multiple unreliable servers. While this queueing model is widely applicable in various research areas even beyond communication networks, this thesis is the first to determine the distribution of the response time in this model. The model evaluation is mainly carried out using Markovian analysis and the method of phases. The obtained quantitative results show that XLMMP is a feasible basis to design scalable wireless sensor networks that (1) may comprise hundreds of thousands of tiny sensor nodes with reduced node complexity, (2) are suitable to monitor an area of tens of square kilometers, (3) achieve a lifetime of several years. The deduced quantifiable relationships between key network parameters — e.g., node size, node density, size of the monitored area, aspired lifetime, and the maximum end-to-end communication delay — enable application-specific optimization of the protocol.}, subject = {Drahtloses Sensorsystem}, language = {en} }