In peer-to-peer networks, finding the appropriate answer for an information request, such as the answer to a query for RDF(S) data, depends on selecting the right peer in the network. We here investigate how social metaphors can be exploited effectively and efficiently to solve this task. To this end, we define a method for query routing, REMINDIN', that lets (i) peers observe which queries are successfully answered by other peers, (ii), memorizes this observation, and, (iii), subsequently uses this information in order to select peers to forward requests to.

This paper addresses the problem of building scalable semantic overlay networks. Our approach follows the principle of data independence by separating a logical layer, the semantic overlay for managing and mapping data and metadata schemas, from a physical layer consisting of a structured peer-to-peer overlay network for e#cient routing of messages. The physical layer is used to implement various functions at the logical layer, including attribute-based search, schema management and schema mapping management. The separation of a physical from a logical layer allows us to process logical operations in the semantic overlay using di#erent physical execution strategies. In particular we identify iterative and recursive strategies for the traversal of semantic overlay networks as two important alternatives. At the logical layer we support semantic interoperability through schema inheritance and semantic gossiping. Thus our system provides a complete solution to the implementation of semantic overlay networks supporting both scalability and interoperability.

This paper describes the design and implementation of Bibster, a Peer-to-Peer system for exchanging bibliographic data among researchers.

Abstract. QoS-based service selection mechanisms will play an essential role in service-oriented architectures, as e-Business applications want to use services that most accurately meet their requirements. Standard approaches in this field typically are based on the prediction of services’ performance from the quality advertised by providers as well as from feedback of users on the actual levels of QoS delivered to them. The key issue in this setting is to detect and deal with false ratings by dishonest providers and users, which has only received limited attention so far. In this paper, we present a new QoS-based semantic web service selection and ranking solution with the application of a trust and reputation management method to address this problem. We will give a formal description of our approach and validate it with experiments which demonstrate that our solution yields high-quality results under various realistic cheating behaviors. 1

Among the open problems in P2P systems, support for non-trivial search predicates, standardized query languages, distributed query processing, query load balancing, and quality of query results have been identified as some of the most relevant issues. This paper describes how range queries as an important non-trivial search predicate can be supported in a structured overlay network that provides O(log n) search complexity on top of a trie abstraction. We provide analytical results that show that the proposed approach is efficient, supports arbitrary granularity of ranges, and demonstrate that its algorithmic complexity in terms of messages is independent of the size of the queried ranges and only depends on the size of the result set. In contrast to other systems which provide evaluation results only through simulations, we validate the theoretical analysis of the algorithms with large-scale experiments on the PlanetLab infrastructure using a fully-fledged implementation of our approach.

Peer-to-peer (p2p) systems are attracting increasing attention as an efficient means of sharing data among large, diverse and dynamic sets of users. The widespread use of XML as a standard for representing and exchanging data in the Internet suggests using XML for describing data shared in a p2p system. However, sharing XML data imposes new challenges in p2p systems related to supporting advanced querying beyond simple keyword-based retrieval. In this paper, we focus on data management issues for processing XML data in a p2p setting, namely indexing, replication, clustering and query routing and processing. For each of these topics, we present the issues that arise, survey related research and highlight open research problems. 1.

Abstract: This paper introduces the NEPOMUK project which aims to create a standard and reference implementation for the Social Semantic Desktop. We outline the requirements and functionalities that were identified for a useful Semantic Desktop system and present an architecture that fulfills these requirements which was acquired by incremental refinement of the architecture of existing Semantic Desktop prototypes. The NEPOMUK project is primarily motivated by three real-life industrial use-cases, we briefly outline these and the processes used to extract required functionalities from the people working in these areas today, and we present a selection of typical tasks where the Semantic Desktop could be of benefit.

Abstract. Non-trivial search predicates beyond mere equality are at the current focus of P2P research. Structured queries, as an important type of non-trivial search, have been studied extensively mainly for unstructured P2P systems so far. As unstructured P2P systems do not use indexing, structured queries are very easy to implement since they can be treated equally to any other type of query. However, this comes at the expense of very high bandwidth consumption and limitations in terms of guarantees and expressiveness that can be provided. Structured P2P systems are an efficient alternative as they typically offer logarithmic search complexity in the number of peers. Though the use of a distributed index (typically a distributed hash table) makes the implementation of structured queries more efficient, it also introduces considerable complexity, and thus only a few approaches exist so far. In this paper we present a first solution for efficiently supporting structured queries, more specifically, XPath queries, in structured P2P systems. For the moment we focus on supporting queries with descendant axes (“//”) and wildcards (“*”) and do not address joins. The results presented in this paper provide foundational basic functionalities to be used by higher-level query engines for more efficient, complex query support. 1

The growing number of web services advocates distributed discovery infrastructures which are semantics-enabled and support quality of service (QoS). In this paper, we introduce a novel approach for semantic discovery of web services in P2P-based registries taking into account QoS characteristics. We distribute (semantic) service advertisements among available registries such that it is possible to quickly identify the repositories containing the best probable matching services. Additionally, we represent the information relevant for the discovery process using Bloom filters and pre-computed matching information such that search efforts are minimized when querying for services with a certain functional/QoS profile. Query results can be ranked and users can provide feedbacks on the actual QoS provided by a service. To evaluate the credibility of these user reports when predicting service quality, we include a robust trust and reputation management mechanism.

Abstract. Full-text search is a challenging problem in Peer-to-Peer (P2P) systems. Currently two promising directions to solve this problem are (1) distributed indexes like hash-tables (DHTs) and (2) semantic overlay networks (SONs) which can be divided into systems that cluster peers with similar content based on term overlap and systems that map both the content and queries on a shared semantic data structure. In this paper we present the pNear system that combines DHTs with clustering via term overlap and show that we are able to tackle some important disadvantages that hold for the individual approaches. We evaluate our approach via simulations based on a large and realistic data-set that we have constructed for this purpose, and which will be useful for similar experiments by others. 1