05 Fakultät Informatik, Elektrotechnik und Informationstechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6

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1995 - 199941

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Start date: 1995End date: 1999

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    A protocol for preserving the exactly-once property of mobile agents
    (1997) Rothermel, Kurt; Straßer, Markus
    Mobile agents are autonomous objects that can migrate from node to node of a computer network. Mobile agent technology has been proposed for various application areas, including electronic commerce, systems management and active messaging. Many of these applications - especially those for electronic commerce - require agents to be performed 'exactly once', independent of communication and node failures. In other words, once a mobile agent has been launched, it must never be lost before its execution is finished. Moreover, each 'portion' of the agent performed at the visited nodes is performed exactly once. Due to the autonomy of mobile agents, there is no 'natural' instance that monitors the progress of an agent's execution. As a result of that agents may be blocked due to node crashes or network partitioning even if there are other nodes available that could continue processing. In this paper, we will describe a protocol that ensures the exactly once property of agents and additionally reduces the blocking probability of agents by introducing so-called observer nodes for monitoring the progress of agents. This protocol is based on conventional transactional technology, such as defined by X/Open DTP or CORBA OTS. It is implemented in the Mole, a mobile agent system developed at Stuttgart University.
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    Task allocation in distributed multimedia systems based on the host-satellite model
    (1998) Dermler, Gabriel; Iqbal, Ashraf
    Multimedia applications require intermediate processing between media sources and sinks. In addition to end-user machines intermediate computers can be used for performing media processing. This possibility leads to the problem of allocating processing components on various computers. In this paper, we study this problem in the context of star-shaped application graphs which have to be allocated between given end-user machines (satellites) and a central computer (host). The problem is formulated in terms of best achievable bottleneck resource usage. Several approaches are considered including anapproximate scheme and two fast-heuristics. Performance measurements show the efficiency of the considered approaches. A discussion of our approach shows important differences to solutions provided for related problems of graph partitioning and mapping.
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    System mechanisms for partial rollback of mobile agent execution
    (1999) Straßer, Markus; Rothermel, Kurt
    Mobile agent technology has been proposed for various fault-sensitive application areas, including electronic commerce, systems management and active messaging. Recently proposed protocols providing the exactly-once execution of mobile agents allow the usage of mobile agents in these application areas. Based on these protocols, a mechanism for the application-initiated partial rollback of the agent execution is presented in this paper. The rollback mechanism uses compensating operations to roll back the effects of the agent execution on the resources and uses a mixture of physical logging and compensating operations to rollback the state of the agent. The introduction of different types of compensating operations and the integration of an itinerary concept with the rollback mechanism allows performance improvements during the agent rollback as well as during the normal agent execution.
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    Makanin's algorithm for solving word equations with regular constraints
    (1998) Diekert, Volker
    We give a self-contained proof of a fundamental result of Makanin (1977), which solves the satisfiability problem of equations with constants over free monoids. Our presentation of Makanin's algorithm is borrows Schulz (1992a), where Makanin's result is extended to the case where solutions are restricted by imposing regular constraints on the variables. This report appears (with minor modifications) as a chapter of the new book of M. Lothaire Algebraic Combinatorics on Words.
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    Visualisierung von Datenbank-Abfragen in Java
    (1999) Engelmann, Ralf
    In vielen Industriefirmen sind Produktionsanlagen mit Datenbanken verbunden, in welchen die anfallenden Prozessdaten gespeichert werden. Diese Prozessdaten werden nach verschiedenen Kriterien mit Hilfe von Datenbank-Abfragen ausgewertet und die Ergebnisse werden grafisch aufbereitet. Die Aufgabe des dieser Arbeit zu Grunde liegenden Projektes war es, solche Prozessdaten durch ein zu entwickelndes Anwendungssystem, basierend auf Java-Technologie in einem WWW-Browser zu präsentieren. CORBA (Common Object Request Broker Architecture) bietet ein standardisiertes Verfahren zur Realisierung verteilter Anwendungen. Die zu entwickelnde Anwendung wurde als verteilte Anwendung auf der Basis einer Three-tier-Anwendungsarchitektur entworfen und mit Hilfe der CORBA-Technologie realisiert. Der Einsatz der CORBA-Technologie in diesem Projekt erlaubt den flexiblen und intelligenten Zugriff auf die Datenbank und die gleichzeitige Verarbeitung der gelesenen Daten. Die Präsentation der aufbereiteten Daten erfolgt in einem Java-Applet, welches in einem WWW-Browser ausgeführt wird und durch die erwähnte CORBA-Technologie die Daten erhält. Dieses Projekt wurde in Zusammenarbeit mit der Industriefirma adstec Automation, Daten- und Systemtechnik GmbH (Oberaichen) durchgeführt.
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    ATOMAS : a transaction-oriented open multi agent system; final report
    (1998) Straßer, Markus; Baumann, Joachim; Hohl, Fritz; Schwehm, Markus; Rothermel, Kurt
    The electronic marketplace of the future will consist of a large number of services located on an open, distributed and heterogeneous platform, which will be used by an even larger number of clients. Mobile Agent Systems are considered to be a precondition for the evolution of such an electronic market. They can provide a flexible infrastructure for this market, i.e. for the installation of new services by service agents as well as for the utilization of these services by client agents. Mobile Agent Systems basically consist of a number of locations and agents. Locations are (logical) abstractions for (physical) hosts in a computer network. The network of locations serves as a unique and homogeneous platform, while the underlying network of hosts may be heterogeneous and widely distributed. Locations therefore have to guarantee independence from the underlying hard- and software. To make the Mobile Agent System an open platform, the system furthermore has to guarantee security of hosts against malicious attacks.
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    Analyse von OODBMS für die technische Modellierung
    (1995) Maile, Annette
    Im Rahmen des Projekts POWER (Product modelling in object-oriented Databases with efficient Methods for Retrieval) werden die Anforderungen an eine integrierte, umfassende Produktdatenmodellierung untersucht und richtungsweisende Konzepte für ganzheitliche, bereichsübergreifende Informationssysteme im CAD/CAM-Bereich entwickelt. Im Rahmen dieser Studienarbeit werden objektorientierte Datenbankmanagementsysteme (OODBMS) daraufhin untersucht, inwieweit sie für die technische Modellierung geeignet sind. Zunächst werden die Anforderungen an eine Produktmodellierung untersucht. Aufgrund der Komplexität technischer Objekte besteht die Notwendigkeit, Objekte nicht nur geometrisch zu modellieren, wie es bei herkömmlichen CAD-Systemen der Fall ist. Zusätzlich müssen die technischen Aspekte modelliert werden, wie z.B. Beziehungen und Funktionen zu anderen Objekten. Ein Lösungsansatz bietet das Konzept der technischen Modellierung, das hier vorgestellt wird. Anhand eines Szenarios aus dem Bereich der technischen Modellierung wird eine Baugruppe konkret modelliert, dabei ist das Szenario stellvertretend für technische Anwendungen anzusehen. Die Baugruppe umfaßt eine Metallscheibe mit einer durchgehenden, mittigen Bohrung und einen symmetrischen, konzentrischen Bohrkranz, sowie eine zugehörige Achse. Trotz der Einfachheit der Baugruppe existieren Beziehungen und Abhängigkeiten der Objekte untereinander. Für die Verwaltung der aus dem Produktmodell entstehenden komplexen Daten werden geeignete Datenbanksysteme benötigt. Im darauffolgenden Kapitel erfolgt eine Einführung in Datenbanksysteme (DBS). Vorgestellt werden die Konzepte von relationalen und objektorientierten DBS. Relationale Datenbanken haben sich im Verwaltungsbereich bewährt. Im technischen Bereich jedoch, wo es sich meist um komplexe Objkete handelt, reichen sie zur Beschreibung dieser nicht aus. Deshalb wird nun eine neue Generation von DBS – die objektorientierten DBS - untersucht. Sie sollen die Unzulänglichkeiten der relationalen DBS beheben. In Kapitel 4 werden die Anforderungen der technischen Modellierung an Datenbanksysteme anhand des Szenarios ermittelt. Die DBS sind u.A. auf Datenstrukturmöglichkeiten, Versions- und Variantenbildung, Darstellung von Beziehungen von Objekten, etc. zu untersuchen. Im Anschluß daran werden diese erarbeiteten Anforderungen in den beiden ausgewählten Datenbanken - Postgres und OBST - evaluiert. Das Ergebnis dieser Analyse ergibt die Bewertung der Eignung und Leistungsfähigkeit der beiden DBS für die technische Modellierung. Abschließend werden die beiden Datenbanken gegenübergestellt und Stärken und Schwächen der Systeme herausgestellt. Die Durchführung der Arbeit erfolgt an HP-Workstations der Serie 9000/700. Zur Verfügung standen die Versionen Postgres 4.01 und OBST 3-4.
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    An agent based framework for the transparent distribution of computations
    (1999) Straßer, Markus; Baumann, Joachim; Schwehm, Markus
    A mobile agent based framework for the transparent distribution and concurrent execution of computations is presented. The framework uses design patterns like the master-slave, abstract factory or the strategy pattern. The architecture of the framework is built on top of a mobile agent system. A performance model allows to identify performance bottlenecks and unbalanced situations within the framework. The framework has been implemented and tested on top of the mobile agent system Mole.
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    A framework for cooperative object recognition
    (1999) Oswald, Norbert; Levi, Paul
    This paper explores the problem of object recognition from multiple observers. The basic idea is to overcome the limitations of the recognition module by integrating information from multiple sources. Each observer is capable of performing appearance-based object recognition, and through knowledge of their relative positions and orientations, the observerrs can coordinate their hypotheses to make object recognition more robust. A framework is proposed for appearance-based object recognition using Canny edge maps that are effectively normalized to be translation and scale invariant. Object matching is formulated as a non-parametric statistical similarity computation between two distribution functions, while information integration is performed in a Bayesian belief net framework. Such nets enable both a continuous and a cooperative consideration of recognition result. Experiments which are reported on two observers recognizing mobile robots show a significant improvent of the recognition results.
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    The shadow approach : an orphan detection protocol for mobile agents
    (1998) Baumann, Joachim; Rothermel, Kurt
    Orphan detection in distributed systems is a well researched field for which many solutions exist. These solutions exploit well defined parent-child relationships given in distributed systems. But they are not applicable in mobile agent systems, since no similar natural relationship between agents exist. Thus new protocols have to be developed. In this paper one such protocol for controlling mobile mobile agents and for orphan detection is presented. The shadow' approach presented in this paper uses the idea of a placeholder (shadow) which is assigned by the agent system to each new agent. This defines an artificial relationship between agents and shadow. The shadow records the location of all dependent agents. Removing the root shadow implies that all dependent agents are declared orphan and are eventually terminated. We introduce agent proxies that create a path from shadow to every agent. In an extension of the basic protocol we additionally allow the shadow to be mobile. The shadow approach can be used for termination of groups of agents even if the exact location of each single agent is not known.