Philipp Obreiter

Towards scalability in tuple spaces

Applications in eCommerce and Ubiquitous Computing ask for coordination of highly distributed and heterogenous data sources and services. Tuple spaces offer a data-driven coordination model, hence they may be used for this purpose. However, research on distributed tuple spaces has not resolved yet how to render tuple spaces scalable. This is partly due to their informal conception. This paper formalizes tuple spaces and introduces a new concept for achieving scalability. It generalizes existing concepts and may lead to scalability in some application areas.

A Case for Evidence-Aware Distributed Reputation Systems

Reputation systems support trust formation in artificial societies by keeping track of the behavior of autonomous entities. In the absence of any commonly trusted entity, the reputation system has to be distributed to the autonomous entities themselves. They may cooperate by issuing recommendations of other entities’ trustworthiness. At the time being, distributed reputation systems rely on plausibility for assessing the truthfulness and consistency of such recommendations. In this paper, we point out the limitations of such plausibility considerations and present an alternative concept that is based on evidences. The concept combines the strengths of non-repudiability and distributed reputation systems. We analyze the issues that are related to the issuance and gathering of evidences. In this regard, we identify four patterns of how evidence-awareness overcomes the limitations of plausibility considerations.

A taxonomy of incentive patterns

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Incentives Patterns . . . . . . . . . . . . . . . . . . . . . . . . 22.1 Relevance of Incentive Patterns . . . . . . . . . . . . . 32.2 Economic Incentive Patterns . . . . . . . . . . . . . . 32.3 General Characteristics of Incentive Patterns . . . . . 43 Trust Based Incentive Patterns . . . . . . . . . . . . . . . . . 63.1 The Collective Pattern . . . . . . . . . . . . . . . . . . 63.2 The Community Pattern . . . . . . . . . . . . . . . . . 74 Trade Based Incentive Patterns . . . . . . . . . . . . . . . . . 84.1 Immediate Action in Return . . . . . . . . . . . . . . 84.2 Deferred Action in Return . . . . . . . . . . . . . . . . 105 Taxonomy and Characteristics of Incentive Patterns . . . . . 145.1 A Taxonomy of Incentive Patterns . . . . . . . . . . . 145.2 Characteristics of Incentive Patterns . . . . . . . . . . 146 Incentive Patterns for DIANE: A Case Study . . . . . . . . . 166.1 Specifics of the Application Environment . . . . . . . 176.2 Applicable Incentive patterns for DIANE . . . . . . . 177 Related Work and Contribution . . . . . . . . . . . . . . . . . 198 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Acknowledgement 22Bibliography 23Glossary 26I

Stepwise Refinable Service Descriptions: Adapting DAML-S to Staged Service Trading

In order for service-oriented architectures to become successful, powerful mechanisms are needed that allow service requestors to find service offerers that are able to provide the services they need. Typically, this service trading needs to be executed in several stages as the offer descriptions are not complete in most cases and different parameters have to be supplemented by the service requestor and offerer alternately. Unfortunately, existing service description languages (like DAML-S) treat service discovery as a one shot activity rather than as a process and accordingly do not support this stepwise refinement. Therefore, in this paper, we introduce the concept of partially instantiated service descriptions containing different types of variables which are instantiated successively, thereby mirroring the progress in a trading process. Moreover, we present possibilities how to integrate these concepts into DAML-S syntactically.

Activity-Based User Modeling in Service-Oriented Ad-Hoc-Networks

Wireless network research still lacks methods to integratively evaluate the performance that can be expected from application layer protocols. The user behavior is predominantly affecting network performance and shows itself in two parts: its mobility and its network usage. However, it is often reduced to analytical mobility models and network traffic models separating otherwise intertwined parameters. This paper demonstrates that the use of an integrated view based on the users’ real-world activity can explain network-relevant parameters both with respect to mobility and to network usage and thereby allows a more natural and realistic modeling of user behavior. The benefits are presented with the help of our graph-based mobility model and its accompanying network usage model.

Engineering incentive schemes for ad hoc networks

In ad hoc networks, devices have to cooperate in order to compensate for the absence of infrastructure Yet, autonomous devices tend to abstain from cooperation in order to save their own resources Incentive schemes have been proposed as a means of fostering cooperation under these circumstances In order to work effectively, incentive schemes need to be carefully tailored to the characteristics of the cooperation protocol they should support This is a complex and demanding task However, up to now, engineers are given virtually no help in designing an incentive scheme Even worse, there exists no systematic investigation into which characteristics should be taken into account and what they imply Therefore, in this paper, we propose a systematic approach for the engineering of incentive schemes The suggested procedure comprises the analysis and adjustment of the cooperation protocol, the choice of appropriate incentives for cooperation, and guidelines for the evaluation of the incentive scheme Finally, we show how the proposed procedure is successfully applied to a service discovery overlay.

Robust and fair trading in volatile environments: overcoming technical problems and uncooperativeness

The exchange of electronic information, goods or functionality is an attractive application for mobile ad-hoc networks. However, users will only take part in such systems, if the probability of a successful exchange is high enough. Exchanges may fail either because of communication failures or due to unfair behavior. Both obstacles need to be overcome to achieve a viable system. Existing approaches tend to address one or the other of the problems, ignoring the second one. In contrast, we present an integrated approach and argue that this is more powerful than two isolated solutions. Replicated transaction logs are used to overcome disconnection periods and an evidence-based distributed reputation system is used to encourage fair behavior. The concepts are implemented as middle-ware components and thoroughly evaluated. The evaluation shows that the system is viable in a wide range of realistic settings.

The interactive cooperation tournament: how to identify opportunities for selfish behavior of computational entities

Distributed reputation systems are a self-organizing means of supporting trusting decisions. In general, the robustness of distributed reputation systems to misbehavior is evaluated by the means of computer based simulation. However, the fundamental issue arises of how to anticipate kinds of successful misbehavior. Existing work in this field approaches this issue in an ad-hoc manner. Therefore, in this paper, we propose a methodology that is based on interactive simulation with human subjects. The requirements for such interaction are discussed. We show how they are met by the Interactive Cooperation Tournament, a simulation environment for identifying promising counter-strategies to the distributed reputation system EviDirs which is showcased in our demo.