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 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 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 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 A fine-grained addressing concept for GeoCast(2001) Coschurba, Peter; Rothermel, KurtGeoCast provides the functionality of sending messages to everyone in a specific area. So far, only the addressing of larger two-dimensional areas was possible. For the use in an urban environment it is crucial that small and three-dimensional areas can be addressed. For example, GeoCast can then be used to send lecture notes to all in a classroom. In this paper we describe a fine-grained addressing concept for GeoCast that supports such areas. In addition we present an architecture that allows the use of that addressing concept together with the GeoRouting-approach developed by Navas and Imielinski. We also present some modifications necessary to enhance the scalability of GeoCast.Item Open Access AIDA II - Abschlußbericht(2000) Hohl, Fritz; Baumann, Joachim; Rothermel, Kurt; Schwehm, Markus; Theilmann, WolfgangIn diesem Bericht geht es um die Zusammenfassung der Erkenntnisse, die im Verlauf der zweiten Phase des AIDA-Projektes von März 1998 bis Februar 2000 gewonnen wurden. AIDA ist ein Projekt, das von der Deutschen Forschungsgemeinschaft (DFG) finanziert wird. Das Thema dieses Projektes sind Systemmechanismen zur Unterstützung mobiler Agenten, also Einheiten, die aus Code, Daten und Zustand bestehen und sich selbstständig in einem Netzwerk bewegen können. Die Ziele von AIDA II waren die Erarbeitung des Themenbereichs Sicherheit in Mobile-Agenten-Systemen mit Schwerpunkt auf der Sicherheit mobiler Agenten gegenüber böswilligen Hosts, die Implementierung von Terminierungsprotokollen und Waisenerkennungsmechanismen, Abrechnungsmechanismen und schließlich Mechanismen zur Strukturunterstützung für Agentenanwendungen.Item Open Access Architecture of a large scale location service(2001) Leonhardi, Alexander; Rothermel, KurtMany mobile applications require some knowledge about the current geographic locations of the mobile objects involved. Therefore, services exist that can store and retrieve the position of mobile objects in an efficient and scalable way. More advanced location-aware applications, however, require additional functionality, like determining all mobile objects inside a certain geographic area (range query). This functionality is not supported by existing services on a large scale yet. In this paper, we present a generic large-scale location service. We describe the location service model, defining the semantics of position, range and nearest neighbor queries. A hierarchical distributed architecture is presented, which can efficiently process these queries, and the structure of a main-memory database for efficiently storing and retrieving position information on a location server. Finally, through measurements on a first prototype of this architecture, we show the feasibility of such a location service.Item Open Access Adressierung und Semantik von geographischen Nachrichten(2001) Coschurba, PeterIn den letzten Jahren haben mobile Computer eine große Verbreitung gefunden. Zur gleichen Zeit wurden Systeme zur Ortsbestimmung (z.B. GPS) auch für normale Anwender verfügbar. Schnell wurde klar, daß eine Kombination dieser beiden Technologien einen deutlichen Mehrwert für die Nutzer bieten kann. Wenn die Information über den aktuellen Aufenthaltsort des Nutzers vorhanden ist, liegt es nahe diese auch für die Kommunikation zu verwenden. Ähnlich wie beim Multicast ist es auch beim sogenannten GeoCast möglich, mehreren Empfängern eine Nachricht zukommen zu lassen. Nur müssen die Empfänger beim GeoCast keiner Gruppe beitreten. Der Sender spezifiziert viel mehr das Zielgebiet der Nachricht, und alle potentiellen Empfänger, die sich in diesem Gebiet befinden, erhalten die Nachricht. Im Bereich GeoCast sind vor allem zwei Bereiche noch nicht intensiv betrachtet worden. Zum einen ist die Frage der Adressierung des Zielgebietes noch offen. Also wie sehen die Adressierungskonzepte aus, mit denen ein Sender das Zielgebiet spezifizieren kann. Die andere Frage die noch nicht sauber betrachtet wurde, ist die Semantik. Welche Semantik hat eine geographische Nachricht. Was sind Alternativen, und warum sind welche Alternativen am sinnvollsten. Diese Fragen sollen in dieser Arbeit näher betrachtet werden.Item Open Access Event management for mobile users(2004) Bauer, MartinThis technical report presents the results of the project "Event Management for Mobile Users", a research cooperation between Universität Stuttgart and Microsoft. In Vienna, Microsoft chief executive Bill Gates recently expressed his vision of a seamless interaction of different computing devices, from PC to mobile phone, that proactively support the users wherever they go. Among other things, he said: "For example, if you want to be notified about something that's changing, that's important to you, software should know which device you have with you and should know what you're doing, know the context to understand if interrupting you with this new information is appropriate or not." (Bill Gates, January 28, 2004, [Los Angeles Times 2004]) This project may present one step towards realizing his vision. It is about event support for mobile users. Depending on their current context, they want to be informed about events that occur in the world around them - the physical as well as the virtual world of digital information systems. So, to optimally support its users, future generations of web services will need information about the real-world context of the user, especially their spatial context. This project was carried out in close cooperation with the Nexus project at Universität Stuttgart, whose goal is to support mobile context-aware applications based on a distributed spatial world model. Events of special interest in this context are spatial events, i.e. events that occur when a certain spatial constellation of objects is reached, e.g. when two people meet or when a customer enters a shopping mall. As the underlying world model is distributed, the events have to be observed on a distributed model. The number of potential spatial events is not restricted, e.g. the event that a user enters an area could be of interest for arbitrary areas. Also, as the spatial world model is distributed over many servers, a local observation is no longer sufficient. Therefore, the well-known publish-subscribe paradigm, in which the observation occurs implicitly within local observers, has to be extended. We propose an observation-notification paradigm, in which the observation of events has to be explicitly initiated by interested clients. The event service that conforms to the new paradigm consists of two components: an observation service, which observes events through a distributed model, and a notification service, which efficiently delivers event notifications. This paradigm applies to all scenarios in which the data needed for the observation of events is distributed over multiple sources. The user wants the specification of events to be as simple and easy as possible. He only wants to specify what event is to be observed, not how the observation of the event is realized. Therefore the distribution aspects should be transparent to the user. However, these aspects have a strong influence on the accuracy of the model and thereby directly affect the accuracy of event observation. We propose that the user specifies an event as a predicate, which becomes true when the event has occurred, plus a threshold probability. If the probability that the event has occurred is above the threshold probability, the event is considered to have occurred and an event notification is sent. The above sketched solution requires calculating the probability with which an event has occurred. We first show which parameters influence the accuracy of the data. We then present update protocols that guarantee a certain accuracy of data in the observer model, i.e. the model where the event is actually observed. Finally we show, how the occurrence probability can be calculated. Based on the identified parameters, the placement of the observation in the system can also be optimized with regard to the accuracy of the data. We have implemented the event service and integrated it into the Nexus platform. As the Nexus platform is intended as an open platform with possibly world-wide scale, scalability, efficiency and interoperability have been important requirements for the design of the components. To support interoperability, we have built on standard technologies like XML, HTTP and SOAP. The evaluation of the event service within the Nexus context shows the feasibility of the approach. We were able to show that the event service performs adequately in certain example scenarios. Experiments with a large-scale scenario are the next steps on our agenda.Item Open Access Final report of design workshop : (10.-15.7.2000)(2000) Nicklas, Daniela; Mitarbeiter der Forschergruppe NexusThis document is the final report of the first design workshop of the NeXus research group of the University of Stuttgart, held from 10th to 15th July 2000. It contains a basic description of the Nexus platform, which is an open, global infrastructure for mobile, spatially aware applications.