05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
Browse
84 results
Search Results
Item Open Access A protocol for preserving the exactly-once property of mobile agents(1997) Rothermel, Kurt; Straßer, MarkusMobile 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.Item Open Access Reachability analysis of multithreaded software with asynchronous communication(2005) Bouajjani, Ahmed; Esparza, Javier; Schwoon, Stefan; Strejcek, JanWe 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.Item Open Access Abstract syntax of WS-BPEL 2.0(2008) Kopp, Oliver; Mietzner, Ralph; Leymann, FrankWS-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.Item Open Access A context-aware hoarding mechanism for location-dependent information systems(2000) Kubach, Uwe; Rothermel, KurtWhen 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.Item Open Access Application sharing in teaching context with wireless networks(2001) Burger, Cora; Papakosta, Stella; Rothermel, KurtThe 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.Item Open Access The design and implementation of a presentation system for interactive 3D graphics applications(2005) Stegmaier, Simon; Klein, Thomas; Strengert, Magnus; Ertl, ThomasWe present the design and implementation of a stand-alone system for presenting interactive 3D graphics applications and arbitrary multimedia contents to a public audience. The description includes technical details regarding the construction of a sturdy case to accommodate touchscreen, PC, video projector, and sound equipment, and details involved in the design of the presentation software. The presented system was evaluated during a week-long exhibition with several hundreds of users.Item Open Access Efficient algorithms for alternating pushdown systems : application to certificate chain discovery with threshold subjects(2006) Suwimonteerabuth, Dejvuth; Schwoon, Stefan; Esparza, JavierMotivated by recent applications of pushdown systems to computer security problems, we present an efficient algorithm for the reachability problem of alternating pushdown systems. Although the algorithm is exponential, a careful analysis reveals that the exponent is usually small in typical applications. We show that the algorithm can be used to compute winning regions in pushdown games. In a second contribution, we observe that the algorithm runs in polynomial time for a certain subproblem, and show that the computation of certificate chains with threshold certificates in the SPKI/SDSI authorization framework can be reduced to this subproblem. We present a detailed complexity analysis of the algorithm and its application, and report on experimental results obtained with a prototype implementation.Item Open Access Makanin's algorithm for solving word equations with regular constraints(1998) Diekert, VolkerWe 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.Item Open Access An agent based framework for the transparent distribution of computations(1999) Straßer, Markus; Baumann, Joachim; Schwehm, MarkusA 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.Item Open Access ATOMAS : a transaction-oriented open multi agent system; final report(1998) Straßer, Markus; Baumann, Joachim; Hohl, Fritz; Schwehm, Markus; Rothermel, KurtThe 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.