05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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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 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 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 Task allocation in distributed multimedia systems based on the host-satellite model(1998) Dermler, Gabriel; Iqbal, AshrafMultimedia 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.Item Open Access Spatial aware geographic Forwarding for mobile ad hoc networks(2002) Tian, Jing; Stepanov, Illya; Rothermel, KurtStateless greedy forwarding based on physical positions of nodes is considered to be more scalable than conventional topology-based routing. However, the stateless nature of geographic forwarding also prevents it from predicting holes in node distribution. Thus, frequent topology holes can significantly degrade the performance of geographic forwarding. So far the approaches mostly depend on excessive state maintenance at nodes to avoid forwarding failures at topology holes. In this paper, we propose and analyse spatial aware geographic forwarding (SAGF), a new approach that proactively avoids constant topology holes caused by spatial constraints while still preserving the advantage of stateless forwarding. Geographic source routes (GSR) based on intermediate locations are selected to bypass topology holes. Proactive route selection based on the spatial knowledge is a general approach, and thus can be used with any geographic forwarding algorithms. We evaluate our approach by extending greedy forwarding with spatial knowledge. Simulation results comparing with GPSR show that even simple spatial information can effectively improve the performance of geographic forwarding.Item Open Access System mechanisms for partial rollback of mobile agent execution(1999) Straßer, Markus; Rothermel, KurtMobile 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.Item Open Access Laws for rewriting queries containing division operators(2005) Rantzau, Ralf; Mangold, ChristophRelational division, also known as small divide, is a derived operator of the relational algebra that realizes a many-to-one set containment test, where a set is represented as a group of tuples: Small divide discovers which sets in a dividend relation contain all elements of the set stored in a divisor relation. The great divide operator extends small divide by realizing many-to-many set containment tests. It is also similar to the set containment join operator for schemas that are not in first normal form. Neither small nor great divide has been implemented in commercial relational database systems although the operators solve important problems and many efficient algorithms for them exist. We present algebraic laws that allow rewriting expressions containing small or great divide, illustrate their importance for query optimization, and discuss the use of great divide for frequent itemset discovery, an important data mining primitive. A recent theoretic result shows that small divide must be implemented by special purpose algorithms and not be simulated by pure relational algebra expressions to achieve efficiency. Consequently, an efficient implementation requires that the optimizer treats small divide as a first-class operator and possesses powerful algebraic laws for query rewriting.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.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 A framework for cooperative object recognition(1999) Oswald, Norbert; Levi, PaulThis 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.