Semantic network analysis of ontologies

A key argument for modeling knowledge in ontologies is the easy re-use and re-engineering of the knowledge. However, beside consistency checking, current ontology engineering tools provide only basic functionalities for analyzing ontologies. Since ontologies can be considered as (labeled, directed) graphs, graph analysis techniques are a suitable answer for this need. Graph analysis has been performed by sociologists for over 60 years, and resulted in the vivid research area of Social Network Analysis (SNA). While social network structures in general currently receive high attention in the Semantic Web community, there are only very few SNA applications up to now, and virtually none for analyzing the structure of ontologies. We illustrate in this paper the benefits of applying SNA to ontologies and the Semantic Web, and discuss which research topics arise on the edge between the two areas. In particular, we discuss how different notions of centrality describe the core content and structure of an ontology. From the rather simple notion of degree centrality over betweenness centrality to the more complex eigenvector centrality based on Hermitian matrices, we illustrate the insights these measures provide on two ontologies, which are different in purpose, scope, and size.

Evolving Distributed Algorithms with Genetic Programming

Distributed systems are one of the most vital components of the economy. The most prominent example is probably the internet, a constituent element of our knowledge society. During the recent years, the number of novel network types has steadily increased. Amongst others, sensor networks, distributed systems composed of tiny computational devices with scarce resources, have emerged. The further development and heterogeneous connection of such systems imposes new requirements on the software development process. Mobile and wireless networks, for instance, have to organize themselves autonomously and must be able to react to changes in the environment and to failing nodes alike. Researching new approaches for the design of distributed algorithms may lead to methods with which these requirements can be met efficiently. In this thesis, one such method is developed, tested, and discussed in respect of its practical utility. Our new design approach for distributed algorithms is based on Genetic Programming, a member of the family of evolutionary algorithms. Evolutionary algorithms are metaheuristic optimization methods which copy principles from natural evolution. They use a population of solution candidates which they try to refine step by step in order to attain optimal values for predefined objective functions. The synthesis of an algorithm with our approach starts with an analysis step in which the wanted global behavior of the distributed system is specified. From this specification, objective functions are derived which steer a Genetic Programming process where the solution candidates are distributed programs. The objective functions rate how close these programs approximate the goal behavior in multiple randomized network simulations. The evolutionary process step by step selects the most promising solution candidates and modifies and combines them with mutation and crossover operators. This way, a description of the global behavior of a distributed system is translated automatically to programs which, if executed locally on the nodes of the system, exhibit this behavior. In our work, we test six different ways for representing distributed programs, comprising adaptations and extensions of well-known Genetic Programming methods (SGP, eSGP, and LGP), one bio-inspired approach (Fraglets), and two new program representations called Rule-based Genetic Programming (RBGP, eRBGP) designed by us. We breed programs in these representations for three well-known example problems in distributed systems: election algorithms, the distributed mutual exclusion at a critical section, and the distributed computation of the greatest common divisor of a set of numbers. Synthesizing distributed programs the evolutionary way does not necessarily lead to the envisaged results. In a detailed analysis, we discuss the problematic features which make this form of Genetic Programming particularly hard. The two Rule-based Genetic Programming approaches have been developed especially in order to mitigate these difficulties. In our experiments, at least one of them (eRBGP) turned out to be a very efficient approach and in most cases, was superior to the other representations.

Entwurf, Implementierung und Evaluation eines modularen Agentensystems zur energieoptimierten Steuerung eines logistischen Automatisierungsprozesses

In dieser Arbeit wird ein modulares Agentensystem entworfen und auf einer marktüblichen PC-basierten SPS-Steuerung implementiert, welches in der Lage ist, den logistischen Anlagenteil eines Hybriden Prozessmodells abhängig von einem dynamischen Energiepreis zu steuern. Dies wird durch die Rekonfiguration und energetische Optimierung der Funktionen einzelner Module auf Grundlage eines Umweltmodells durch Softwareagenten erreicht. Dieses Umweltmodell wird zunächst in verschiedenen Diagrammen der objektorientierten Modellierungssprachen UML und SysML modelliert. Hierfür werden im Rahmen dieser Arbeit dazu notwendige Erweiterungen des Timing-Diagramms der UML entworfen. Das Agentensystem wird mit der Methode Gaia entworfen. Durch das in dieser Methode enthaltene Rollenkonzept werden Möglichkeiten zur Wiederverwendung von Teilen des Entwurfs auch innerhalb von anderen Arbeiten ermöglicht. Die Echtzeitanforderungen, welche sich an die Steuerungssoftware des logistischen Prozesses ergeben, können bei dem Entwurf durch Gaia modelliert werden. Das im Vorgehen nach Gaia enthaltene Bekanntschaftsmodell wird um die Darstellung weiterer wichtiger Informationen erweitert.

CD-Systems of Restarting Automata Governed by Explicit Enable and Disable Conditions

We introduce a new mode of operation for CD-systems of restarting automata by providing explicit enable and disable conditions in the form of regular constraints. We show that, for each CD-system M of restarting automata and each mode m of operation considered by Messerschmidt and Otto, there exists a CD-system M' of restarting automata of the same type as M that, working in the new mode ed, accepts the language that M accepts in mode m. Further, we prove that in mode ed, a locally deterministic CD-system of restarting automata of type RR(W)(W) can be simulated by a locally deterministic CD-system of restarting automata of the more restricted type R(W)(W). This is the first time that a non-monotone type of R-automaton without auxiliary symbols is shown to be as expressive as the corresponding type of RR-automaton.

A Modeling Analysis of Changing Global Land Use as affected by Changing Demands for Wood Products

The 21st century has brought new challenges for forest management at a time when globalization in world trade is increasing and global climate change is becoming increasingly apparent. In addition to various goods and services like food, feed, timber or biofuels being provided to humans, forest ecosystems are a large store of terrestrial carbon and account for a major part of the carbon exchange between the atmosphere and the land surface. Depending on the stage of the ecosystems and/or management regimes, forests can be either sinks, or sources of carbon. At the global scale, rapid economic development and a growing world population have raised much concern over the use of natural resources, especially forest resources. The challenging question is how can the global demands for forest commodities be satisfied in an increasingly globalised economy, and where could they potentially be produced? For this purpose, wood demand estimates need to be integrated in a framework, which is able to adequately handle the competition for land between major land-use options such as residential land or agricultural land. This thesis is organised in accordance with the requirements to integrate the simulation of forest changes based on wood extraction in an existing framework for global land-use modelling called LandSHIFT. Accordingly, the following neuralgic points for research have been identified: (1) a review of existing global-scale economic forest sector models (2) simulation of global wood production under selected scenarios (3) simulation of global vegetation carbon yields and (4) the implementation of a land-use allocation procedure to simulate the impact of wood extraction on forest land-cover. Modelling the spatial dynamics of forests on the global scale requires two important inputs: (1) simulated long-term wood demand data to determine future roundwood harvests in each country and (2) the changes in the spatial distribution of woody biomass stocks to determine how much of the resource is available to satisfy the simulated wood demands. First, three global timber market models are reviewed and compared in order to select a suitable economic model to generate wood demand scenario data for the forest sector in LandSHIFT. The comparison indicates that the ‘Global Forest Products Model’ (GFPM) is most suitable for obtaining projections on future roundwood harvests for further study with the LandSHIFT forest sector. Accordingly, the GFPM is adapted and applied to simulate wood demands for the global forestry sector conditional on selected scenarios from the Millennium Ecosystem Assessment and the Global Environmental Outlook until 2050. Secondly, the Lund-Potsdam-Jena (LPJ) dynamic global vegetation model is utilized to simulate the change in potential vegetation carbon stocks for the forested locations in LandSHIFT. The LPJ data is used in collaboration with spatially explicit forest inventory data on aboveground biomass to allocate the demands for raw forest products and identify locations of deforestation. Using the previous results as an input, a methodology to simulate the spatial dynamics of forests based on wood extraction is developed within the LandSHIFT framework. The land-use allocation procedure specified in the module translates the country level demands for forest products into woody biomass requirements for forest areas, and allocates these on a five arc minute grid. In a first version, the model assumes only actual conditions through the entire study period and does not explicitly address forest age structure. Although the module is in a very preliminary stage of development, it already captures the effects of important drivers of land-use change like cropland and urban expansion. As a first plausibility test, the module performance is tested under three forest management scenarios. The module succeeds in responding to changing inputs in an expected and consistent manner. The entire methodology is applied in an exemplary scenario analysis for India. A couple of future research priorities need to be addressed, particularly the incorporation of plantation establishments; issue of age structure dynamics; as well as the implementation of a new technology change factor in the GFPM which can allow the specification of substituting raw wood products (especially fuelwood) by other non-wood products.

On CD-systems of stateless deterministic R-automata with window size one

We study cooperating distributed systems (CD-systems) of restarting automata that are very restricted: they are deterministic, they cannot rewrite, but only delete symbols, they restart immediately after performing a delete operation, they are stateless, and they have a read/write window of size 1 only, that is, these are stateless deterministic R(1)-automata. We study the expressive power of these systems by relating the class of languages that they accept by mode =1 computations to other well-studied language classes, showing in particular that this class only contains semi-linear languages, and that it includes all rational trace languages. In addition, we investigate the closure and non-closure properties of this class of languages and some of its algorithmic properties.

Der „elektronische Personalausweis“ in Deutschland: Gesetzgebungsverfahren, Einflussfaktoren und Pfade

Zum 1. November 2010 wird in Deutschland der neue Personalausweis starten, der gegenüber dem bisherigen Dokument drei neue Funktionen enthält: Die Speicherung biometrischer Daten, die optionale Signaturfunktion und den elektronischen Identitätsnachweis, also eine technische Funktion zur elektronischen Authentisierung. Die Rechtsgrundlagen wurden mit der Verabschiedung des neuen Gesetzes über Personalausweise und den elektronischen Identitätsnachweis sowie zur Änderung weiterer Vorschriften am 18. Dezember 2008 im Bundestag gelegt. Wie bei anderen Gesetzgebungsverfahren sind diesem formalen Verfahren wissenschaftliche und politische, in diesem Fall auch technische, Diskussionen vorangegangen, die darüber hinaus während des Gesetzgebungsverfahrens fortgesetzt wurden. Die Studie beschreibt in einem ersten Schritt die Eckdaten und wesentlichen Inhalte der Diskussion und des Gesetzgebungsverfahrens. Im Anschluss erfolgt eine Darlegung einzelner Einflussfaktoren und „Pfade“ der rechtlichen, technischen und politischen Entwicklung, die Einfluss auf bestimmte Innovationsentscheidungen hatten. Daran schließt sich eine Betrachtung der einzelnen Akteure an, bevor der Gesamtprozess bewertet wird.

20. Theorietag der GI-Fachgruppe "Automaten und Formale Sprachen''

Die Fachgruppe AFS (früher Fachgruppe 0.1.5) der Gesellschaft für Informatik veranstaltet seit 1991 einmal im Jahr ein Treffen der Fachgruppe im Rahmen eines Theorietags, der traditionell eineinhalb Tage dauert. Seit dem Jahr 1996 wird dem eigentlichen Theorietag noch ein eintägiger Workshop zu speziellen Themen der theoretischen Informatik vorangestellt. In diesem Jahr wurde der Theorietag vom Fachgebiet "Theoretische Informatik" des Fachbereichs Elektrotechnik/Informatik der Universität Kassel organisiert. Er fand vom 29.9. bis 1.10.2010 in Baunatal bei Kassel statt. Dabei stand der begleitende Workshop unter dem allgemeinen Thema "Ausgewählte Themen der Theoretischen Informatik". Als Vortragende für diesen Workshop konnten Carsten Damm (Göttingen), Markus Holzer (Giessen), Peter Leupold (Kassel), Martin Plátek (Prag) und Heribert Vollmer (Hannover) gewonnen werden. Das Programm des eigentlichen Theorietags bestand aus 20 Vorträgen sowie der Sitzung der Fachgruppe AFS. In diesem Band finden sich die Zusammenfassungen aller Vorträge sowohl des Workshops als auch des Theorietags. Desweiteren enthält er das Programm und die Liste aller Teilnehmer.

A Framework for TEI-Based Scholarly Text Editions

In this paper, we describe an interdisciplinary project in which visualization techniques were developed for and applied to scholarly work from literary studies. The aim was to bring Christof Schöch's electronic edition of Bérardier de Bataut's Essai sur le récit (1776) to the web. This edition is based on the Text Encoding Initiative's XML-based encoding scheme (TEI P5, subset TEI-Lite). This now de facto standard applies to machine-readable texts used chiefly in the humanities and social sciences. The intention of this edition is to make the edited text freely available on the web, to allow for alternative text views (here original and modern/corrected text), to ensure reader-friendly annotation and navigation, to permit on-line collaboration in encoding and annotation as well as user comments, all in an open source, generically usable, lightweight package. These aims were attained by relying on a GPL-based, public domain CMS (Drupal) and combining it with XSL-Stylesheets and Java Script.

Echtzeitsimulation großer Grafikmodelle

Die vorliegende Arbeit entstand während meiner Zeit als wissenschaftlicher Mitarbeiter im Fachgebiet Technische Informatik an der Universität Kassel. Im Rahmen dieser Arbeit werden der Entwurf und die Implementierung eines Cluster-basierten verteilten Szenengraphen gezeigt. Bei der Implementierung des verteilten Szenengraphen wurde von der Entwicklung eines eigenen Szenengraphen abgesehen. Stattdessen wurde ein bereits vorhandener Szenengraph namens OpenSceneGraph als Basis für die Entwicklung des verteilten Szenengraphen verwendet. Im Rahmen dieser Arbeit wurde eine Clusterunterstützung in den vorliegenden OpenSceneGraph integriert. Bei der Erweiterung des OpenSceneGraphs wurde besonders darauf geachtet den vorliegenden Szenengraphen möglichst nicht zu verändern. Zusätzlich wurde nach Möglichkeit auf die Verwendung und Integration externer Clusterbasierten Softwarepakete verzichtet. Für die Verteilung des OpenSceneGraphs wurde auf Basis von Sockets eine eigene Kommunikationsschicht entwickelt und in den OpenSceneGraph integriert. Diese Kommunikationsschicht wurde verwendet um Sort-First- und Sort-Last-basierte Visualisierung dem OpenSceneGraph zur Verfügung zu stellen. Durch die Erweiterung des OpenScenGraphs um die Cluster-Unterstützung wurde eine Ansteuerung beliebiger Projektionssysteme wie z.B. einer CAVE ermöglicht. Für die Ansteuerung einer CAVE wurden mittels VRPN diverse Eingabegeräte sowie das Tracking in den OpenSceneGraph integriert. Durch die Anbindung der Geräte über VRPN können diese Eingabegeräte auch bei den anderen Cluster-Betriebsarten wie z.B. einer segmentierten Anzeige verwendet werden. Die Verteilung der Daten auf den Cluster wurde von dem Kern des OpenSceneGraphs separat gehalten. Damit kann eine beliebige OpenSceneGraph-basierte Anwendung jederzeit und ohne aufwendige Modifikationen auf einem Cluster ausgeführt werden. Dadurch ist der Anwender in seiner Applikationsentwicklung nicht behindert worden und muss nicht zwischen Cluster-basierten und Standalone-Anwendungen unterscheiden.

Information Exchange and Fusion in Dynamic and Heterogeneous Distributed Environments

Context awareness, dynamic reconfiguration at runtime and heterogeneity are key characteristics of future distributed systems, particularly in ubiquitous and mobile computing scenarios. The main contributions of this dissertation are theoretical as well as architectural concepts facilitating information exchange and fusion in heterogeneous and dynamic distributed environments. Our main focus is on bridging the heterogeneity issues and, at the same time, considering uncertain, imprecise and unreliable sensor information in information fusion and reasoning approaches. A domain ontology is used to establish a common vocabulary for the exchanged information. We thereby explicitly support different representations for the same kind of information and provide Inter-Representation Operations that convert between them. Special account is taken of the conversion of associated meta-data that express uncertainty and impreciseness. The Unscented Transformation, for example, is applied to propagate Gaussian normal distributions across highly non-linear Inter-Representation Operations. Uncertain sensor information is fused using the Dempster-Shafer Theory of Evidence as it allows explicit modelling of partial and complete ignorance. We also show how to incorporate the Dempster-Shafer Theory of Evidence into probabilistic reasoning schemes such as Hidden Markov Models in order to be able to consider the uncertainty of sensor information when deriving high-level information from low-level data. For all these concepts we provide architectural support as a guideline for developers of innovative information exchange and fusion infrastructures that are particularly targeted at heterogeneous dynamic environments. Two case studies serve as proof of concept. The first case study focuses on heterogeneous autonomous robots that have to spontaneously form a cooperative team in order to achieve a common goal. The second case study is concerned with an approach for user activity recognition which serves as baseline for a context-aware adaptive application. Both case studies demonstrate the viability and strengths of the proposed solution and emphasize that the Dempster-Shafer Theory of Evidence should be preferred to pure probability theory in applications involving non-linear Inter-Representation Operations.

CD-Systems of Stateless Deterministic R(1)-Automata Governed by an External Pushdown Store

We study cooperating distributed systems (CD-systems) of stateless deterministic restarting automata with window size 1 that are governed by an external pushdown store. In this way we obtain an automata-theoretical characterization for the class of context-free trace languages.

On Globally Deterministic CD-Systems of Stateless R-Automata with Window Size One

It is known that cooperating distributed systems (CD-systems) of stateless deterministic restarting automata with window size 1 accept a class of semi-linear languages that properly includes all rational trace languages. Although the component automata of such a CD-system are all deterministic, in general the CD-system itself is not, as in each of its computations, the initial component and the successor components are still chosen nondeterministically. Here we study CD-systems of stateless deterministic restarting automata with window size 1 that are themselves completely deterministic. In fact, we consider two such types of CD-systems, the strictly deterministic systems and the globally deterministic systems.