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Subject: search.filters.subject.004Start date: 2000End date: 2009

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Now showing 1 - 10 of 168
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    A context-aware hoarding mechanism for location-dependent information systems
    (2000) Kubach, Uwe; Rothermel, Kurt
    When used in an outdoor environment mobile information systems often suffer from the disadvantages of wireless WANs, especially low bandwidth, high delay, and frequent disconnections. Hoarding is an effective method to overcome these disadvantages by transferring information which is probably needed by the user in advance. In this paper we propose a generic, context-aware hoarding mechanism. When selecting the information to hoard, it considers the user's future location as well as the expected speed of movement. In contrast to existing hoarding mechanisms it is universally applicable for different types of location-dependent, mobile information systems. Its flexibility allows it to rely on different knowledge sources in order to get information about a user's context.
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    A Bayesian network approach to assess and predict software quality using activity-based quality models
    (2009) Wagner, Stefan
    Assessing and predicting the complex concept of software quality is still challenging in practice as well as research. Activity-based quality models break down this complex concept into more concrete definitions, more precisely facts about the system, process and environment and their impact on activities performed on and with the system. However, these models lack an operationalisation that allows to use them in assessment and prediction of quality. Bayesian Networks (BN) have been shown to be a viable means for assessment and prediction incorporating variables with uncertainty. This paper describes how activity-based quality models can be used to derive BN models for quality assessment and prediction. The proposed approach is demonstrated in a proof of concept using publicly available data.
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    Abstract syntax of WS-BPEL 2.0
    (2008) Kopp, Oliver; Mietzner, Ralph; Leymann, Frank
    WS-BPEL 2.0 is the current version of the "Business Process Execution Language for Web Services". Until now, no formal definition of its syntax exists. We present a complete syntax of WS-BPEL 2.0 of both abstract and executable processes.
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    Application sharing in teaching context with wireless networks
    (2001) Burger, Cora; Papakosta, Stella; Rothermel, Kurt
    The success of teaching is depending on a couple of factors: on how far students are involved into lectures, on the material, its completeness and on co-learning of students. Involvement of students into lectures means, being able to follow the thoughts of the teacher, ask questions and make comments. The material must be presented in a suitable form and essential parts of it have to be available during the whole learning process, for preparing participation in lectures and exercises as well as for exams. For more effective learning and training of social abilities, working in groups of co-learners has to be encouraged. Mobile and ubiquitous computing offer new possibilities to achieve these goals by increasing the awareness in class and supporting an active participation of students. By promoting existing concepts and enabling new ways of application sharing, the project SASCIA (System architecture supporting cooperative and interactive applications) aims at developing a framework for multiple applications to support teaching in collocated, remote and hybrid scenarios. Its core is composed of components to capture and distribute context information about sessions, participants and those applications that are used during a lecture or encounter among students. A configurable floor control was designed to cope with a wide spectrum of applications and learning situations. For some cases, even a control for semantic consistency can be necessary. In combination with a suitable user and session management, a whiteboard for annotations and a recording facility to support latecomers as well as subsequent replay, these components are providing the required functionality. As a consequence, SASCIA offers remote control and viewing facilities to all participants during lectures and co-learning sessions.
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    Fragments of first-order logic over infinite words
    (2009) Diekert, Volker; Kufleitner, Manfred
    We give topological and algebraic characterizations as well as language theoretic descriptions of the following subclasses of first-order logic for omega-languages: Sigma2, FO2, the intersection of FO2 and Sigma2, and Delta2 (and by duality Pi2 and the intersection of FO2 and Pi2). These descriptions extend the respective results for finite words. In particular, we relate the above fragments to language classes of certain (unambiguous) polynomials. An immediate consequence is the decidability of the membership problem of these classes, but this was shown before by Wilke and Bojanczyk and is therefore not our main focus. The paper is about the interplay of algebraic, topological, and language theoretic properties.
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    Reachability analysis of multithreaded software with asynchronous communication
    (2005) Bouajjani, Ahmed; Esparza, Javier; Schwoon, Stefan; Strejcek, Jan
    We introduce asynchronous dynamic pushdown networks (ADPN), a new model for multithreaded programs in which pushdown systems communicate via shared memory. ADPN generalizes both CPS (concurrent pushdown systems) and DPN (dynamic pushdown networks). We show that ADPN exhibit several advantages as a program model. Since the reachability problem for ADPN is undecidable even in the case without dynamic creation of processes, we address the bounded reachability problem, which considers only those computation sequences where the (index of the) thread accessing the shared memory is changed at most a fixed given number of times. We provide efficient algorithms for both forward and backward reachability analysis. The algorithms are based on automata techniques for symbolic representation of sets of configurations.
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    Do code clones matter?
    (2009) Juergens, Elmar; Deißenböck, Florian; Hummel, Benjamin; Wagner, Stefan
    Code cloning is not only assumed to inflate maintenance costs but also considered defect-prone as inconsistent changes to code duplicates can lead to unexpected behavior. Consequently, the identification of duplicated code, clone detection, has been a very active area of research in recent years. Up to now, however, no substantial investigation of the consequences of code cloning on program correctness has been carried out. To remedy this shortcoming, this paper presents the results of a large-scale case study that was undertaken to find out if inconsistent changes to cloned code can indicate faults. For the analyzed commercial and open source systems we not only found that inconsistent changes to clones are very frequent but also identified a significant number of faults induced by such changes. The clone detection tool used in the case study implements a novel algorithm for the detection of inconsistent clones. It is available as open source to enable other researchers to use it as basis for further investigations.
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    Interactive volume rendering in virtual environments
    (2003) Schulze-Döbold, Jürgen Peter; Ertl, Thomas (Prof. Dr.)
    This dissertation is about the interactive visualization of volume data in virtual environments. Only data on regular grids will be discussed. Research was conducted on three major topics: visualization algorithms, user interfaces, and parallelization of the visualization algorithms. Because the shear-warp algorithm is a very fast CPU-based volume rendering algorithm, it was investigated how it could be adapted to the characteristics of virtual environments. This required the support of perspective projection, as well as specific developments for interactive work, for instance a variable frame rate or the application of clipping planes. Another issue was the improvement of image quality by the utilization of pre-integration for the compositing. Concerning the user interface, a transfer function editor was created, which was tailored to the conditions of virtual environments. It should be usable as intuitively as possible, even with imprecise input devices or low display resolutions. Further research was done in the field of direct interaction, for instance a detail probe was developed which is useful to look inside of a dataset. In order to run the user interface on a variety of output devices, a device independent menu and widget system was developed. The shear-warp algorithm was accelerated by a parallelization which is based on MPI. For the actual volume rendering, a remote parallel computer can be employed, which needs to be linked to the display computer via a network connection. Because the image transfer turned out to be the bottleneck of this solution, it is compressed before being transferred. Furthermore, it will be described how all the above developments were combined to a volume rendering system, and how they were integrated into an existing visualization toolkit.
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    Modelling the quality economics of defect-detection techniques
    (2006) Wagner, Stefan
    There are various ways to evaluate defect-detection techniques. However, for a comprehensive evaluation the only possibility is to reduce all influencing factors to costs. There are already some models and metrics for the cost of quality that can be used in that context. These models allow the structuring of the costs but do not show all influencing factors and their relationships. This paper proposes an analytical model for the economics of defect-detection techniques that can be used for analysis and optimisation of the usage of such techniques. In particular we analyse the sensitivity of the model and how the model can be applied in practice.
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    Emulation von Rechnernetzen zur Leistungsanalyse von verteilten Anwendungen und Netzprotokollen
    (2005) Herrscher, Daniel J.; Rothermel, Kurt (Prof. Dr. rer. nat. Dr. h. c)
    Um die Leistung von verteilten Anwendungen und Netzprotokollen in Abhängigkeit von den Eigenschaften der verwendeten Rechnernetze zu analysieren, wird eine Testumgebung benötigt, die Netzeigenschaften zuverlässig nachbilden ("emulieren") kann. Eine solche Testumgebung wird Emulationssystem genannt. Bisher existierende Emulationssysteme sind aufgrund ihrer Architektur entweder nur für sehr kleine Szenarien geeignet, oder sie können nur unabhängige Netzverbindungen nachbilden, und schließen damit alle Netztechnologien mit gemeinsamen Medien aus. In dieser Arbeit werden zunächst verschiedene Architekturvarianten für die Realisierung eines Emulationssystems vorgestellt und bewertet. Für die Variante mit zentraler Steuerung und verteilten Emulationswerkzeugen wird dann detailliert die Funktionalität eines Emulationssystems mit seinen wesentlichen Komponenten beschrieben. Das in dieser Arbeit entwickelte Emulationsverfahren greift auf der logischen Ebene der Sicherungsschicht in den Kommunikationsstapel ein. Auf dieser Ebene werden die beiden Basiseffekte Rahmenverlust und Verzögerung durch verteilte Emulationswerkzeuge nachgebildet. Alle anderen Netzeigenschaften können auf diese Basiseffekte zurückgeführt werden. Um Netztechnologien mit gemeinsamen Medien durch verteilte Werkzeuge nachbilden zu können, wird zusätzlich das Konzept des virtuellen Trägersignals eingeführt. Hierbei werden die Eigenschaften eines Rundsendemediums nachgebildet, indem kooperative Emulationswerkzeuge Rundsendungen zur Signalisierung eines Trägersignals benutzen. Somit kann jedeWerkzeuginstanz lokal ein aktuelles Modell des emulierten gemeinsamen Mediums halten. Auf dieser Basis kann auch das Verhalten von Medienzugriffsprotokollen nachgebildet werden. Die Arbeit deckt auch die wesentlichen Realisierungsaspekte eines Emulationssytems ab. Mit ausführlichen Messungen wird gezeigt, dass das entwickelte System für die Nachbildung von Netzszenarien sehr gut geeignet ist, selbst wenn die nachzubildenden Parameter sich dynamisch ändern. Die entwickelten Werkzeuge sind in der Lage, Netzeigenschaften in einem weiten Parameterbereich realistisch nachzubilden. Mit diesem System steht nun eine ideale Testumgebung für Leistungsmessungen von verteilten Anwendungen und Netzprotokollen in Abhängigkeit von Netzeigenschaften zur Verfügung.