Transaction support is crucial in mobile data management. Specific characteristics of mobile environments (e.g. variable bandwidth, disconnections, limited resources on mobile hosts) make traditional transaction management techniques no longer appropriate. Several models for mobile transactions have been proposed but it is difficult to have an overview of all of them. This paper analyzes and compares several contributions to mobile transactions. The analysis distinguishes two groups of models. The first group includes proposals where transactions are completely or partially executed on mobile hosts. In this group we focus on ACID properties support. The second group considers transactions requested by mobile hosts and executed on the wired network. In this case, ACID properties are not compromised and focus is on supporting mobile host movements during transaction execution. Discussions pointing out limitations, interesting solutions and research perspectives complete this paper.

By decentralizing control, P2P systems provide efficient, scalable data sharing. However, when sharing data for different purposes (e.g., billing, purchase, shipping, etc.), data privacy can be easily violated by untrustworthy peers wich may use data for other purposes (e.g., marketing, fraudulence, profiling, etc.). A basic principle of data privacy is purpose specification which states that data providers should be able to specify the purpose for which their data will be collected and used. In the context of P2P systems, decentralized control makes it hard to enforce purpose-based privacy. And the major problem of data disclosure is not addressed. Hippocratic databases provide mechanisms for enforcing purpose-based disclosure control within a corporation datastore. In this paper, we apply the Hippocratic database principles to P2P systems to enforce purpose-based privacy. We focus on Distributed Hash Tables (DHTs), because they provide strong guarantees in terms of access performance. We propose PriServ, a privacy service which prevents privacy violation by prohibiting malicious data access. The performance evaluation of our approach through simulation shows that the overhead introduced by PriServ is small.

When users need to perform a digital activity, they evaluate available systems according to their functionality, ease of use, QoS, and/or economical aspects. Recently, trust has become another key factor for such evaluation. Two main issues arise in the trust management research community. First, how to define the trust in an entity, knowing that this can be a person, a digital or a physical resource. Second, how to evaluate such value of trust in a system as a whole for a particular activity. Defining and evaluating trust in systems is an open problem because there is no consensus on the used approach. In this work we propose an approach applicable to any kind of system. The distinctive feature of our proposal is that, besides taking into account the trust in the different entities the user depends on to perform an activity, it takes into consideration the architecture of the system to determine its trust level. Our goal is to enable users to have a personal comparison between different systems for the same application needs and to choose the one satisfying their expectations. This paper introduces our approach, which is based on probability theory, and presents ongoing results.

For years, transactional protocols have been defined for particular application needs. Traditionally, when implementing a transaction service, a protocol is chosen and it remains the same during the system execution. Nevertheless, the dynamic nature of nowadays application contexts (e.g., mobile, ad-hoc, peer-to-peer) and behaviour variations (semanticrelated aspects) motivates the needs for application adaptation. Next generation of system applications should be adaptive or even better self-adaptive. This paper proposes (1) a component-based architecture of standard 2PC-based protocols and (2) a self-Adaptive Component-based cOmmit Management, named ACOM. Self-adaptation is obtained by behaviour awareness and component-based reconfiguration. This allows ACOM to select the most appropriate protocol according to the context. We show that using ACOM performs better than using only one commit protocol in a variable system and that the reconfiguration cost can be negligible.

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P2P systems are increasingly used for efficient, scalable data sharing. Popular applications focus on massive file sharing. However, advanced applications such as online communities (e.g., medical or research communities) need to share private or sensitive data. Currently, in P2P systems, untrusted peers can easily violate data privacy by using data for malicious purposes (e.g., fraudulence, profiling). To prevent such behavior, the well accepted Hippocratic database principle states that data owners should specify the purpose for which their data will be collected. In this paper, we apply such principles as well as reputation techniques to support purpose and trust in structured P2P systems. Hippocratic databases enforce purpose-based privacy while reputation techniques guarantee trust. We propose a P2P data privacy model which combines the Hippocratic principles and the trust notions. We also present the algorithms of PriServ, a DHT-based P2P privacy service which supports this model and prevents data privacy violation. We show, in a performance evaluation, that PriServ introduces a small overhead.1 Organization for Economic Co-operation and Development. One of the world's largest and most reliable source of comparable statistics, on economic and social data. http://www.oecd.org/

Abstract. Recently, trust emerged as a momentous aspect to evaluate resources, services or persons. In our work, the trust notion focuses on a system as a whole and from the point of view of a particular user to do a particular digital activity as editing a document, mailing, chatting, etc. Our general goals are (i) to enable users to have a personal comparison of applications allowing them to do an activity such that they can choose the one satisfying their personal expectations and (ii) to know how trustworthy their system is to do a particular activity (all applications together). We consider a system as a graph composed of paths where the source is a person and the target is a final application or data. We consider that trust in a system depends on its architecture and we identify two problems (i) how to evaluate trust in a graph having dependent paths i.e., paths having common nodes, and (ii) how to express and deal with uncertainty in evaluating trust in a system. Concerning the first problem, trust approaches based on graphs have been proposed in the domain of social networks. Their solution for dependent paths is either removing paths or just choosing one of them what causes loss of information. Considering the second problem, subjective logic emerged to express trust as a subjective opinion with a degree of uncertainty. In this paper we present SUBJECTIVETRUST, an approach that relies on subjective logic to evaluate trust in distributed systems. It proposes two solutions to treat dependent paths and takes into account the shape of the system architecture in trust evaluation. We analyze SUBJECTIVETRUST in a series of experiments that show its accuracy.