Super-peer P2P Systems Utilizing Mediated Knowledge-based and User- defined Views

Abstract In recent years, peer-to-peer data integration systems have attracted significant attention for their ability to communicate, collaborate and share information in a networked environment. One of the main problems that arises in such systems is how to exploit their mappings in order to answer queries posed to one peer. Our proposed framework can be used to exploit the existing mapped data together with its data location information for defining a peer’s data view. This data view is expected to produce query results based on peer preferences rather than using standard query processing at the super-peer level, as practiced in current super-peer P2P systems. Our framework consists of two major components: a mediated knowledge base at the super-peer and user-defined data views at the peer. Keywords: Peer-to-peer, User Defined Views, Mediated knowledgebase. 1. Introduction Recently, Peer-to-Peer (P2P) systems have become an active research area because of the opportunities for real-time communication, ad-hoc collaboration and information sharing in a large-scale environment. P2P refers to a class of systems and applications that employ distributed and autonomous nodes (peers) that co-operate in the community to share resources and services [1,2]. As the actual data is stored in various autonomous peers’ data source locations, peers are ‘linked’ to other peers by mappings. Two basic problems arising in this architecture are: how to discover, express and compose the mappings between peers and how to exploit the mappings in order to answer queries posed to one peer [3]. The second problem is studied in this paper. In P2P systems, peers are connected on an ad-hoc basis and the location of information is not controlled by the system. There is no guarantee that a query will be successful, even for the best query language. This is because peers only have local knowledge of the network, within which peer nodes may enter and leave frequently. The most widely known P2P network architectures are pure and super-peer networks. Our work will investigate searching issues in super-peer networks. A search process includes aspects such as the query forwarding method, the set of nodes that receive a query-related message, the form of these messages, local processing, the stored index, and information maintenance [4]. The process depends on the system architecture used. Basically, searching can be classified as blind search, and informed search. Blind search is formally used in pure P2P systems. The original Gnutella [5] algorithm used the blind search method (also known as a flooding scheme) where each posted query is forwarded to all accessible peers within TTL (‘Time-To-Leave’) hops [4]. Super-peer networks use the informed search method because of the function of the super-peer node [6, 7, 8, 9], which can be seen as a hub that receives queries from connected peers (leaves). This query is forwarded to any relevant leaves and also to neighboring hubs based on a query routing table (also known as a super-peer index). The super-peer index retains information about data stored at neighboring peers so that the posted query will be forwarded to relevant peers only, in order to reduce the network traffic. This index would maintain either the actual location of required data as in Gnutella2 [10] or give ‘directions’ towards required data as in ‘Routing Indices’ (RIs) [11]. Hence, the super-peer node becomes the most vital component for query processing in super-peer networks. However, super-peers that provide the index for query routing are burdened by other peer nodes and by having to transform posted queries into sub-queries that become local queries for peers [12]. This project aims to reduce this burden by providing individual peers with the capability to define their own data views so