The success of a P2P file-sharing network highly depends on the scalability and versatility of its search mechanism. Two particularly desirable search features are scope (ability to find infrequent items) and support for partial-match queries (queries that contain typos or include a subset of keywords). While centralized-index architectures (such as Napster) can support both these features, existing decentralized architectures seem to support at most one: prevailing unstructured P2P protocols (such as Gnutella and FastTrack) deploy a "blind" search mechanism where the set of peers probed is unrelated to the query; thus they support partial-match queries but have limited scope. On the other extreme, the recently-proposed distributed hash tables (DHTs) such as CAN and CHORD, couple index location with the item's hash value, and thus have good scope but can not effectively support partial-match queries. Another hurdle to DHTs deployment is their tight control of the overlay structure and the information (part of the index) each peer maintains, which makes them more sensitive to failures and frequent joins and disconnects.

The ability to discover services o#ered in a mobile ad hoc network is the major prerequisite for e#ective usability of these networks. Unfortunately, existing approaches to service trading are not well suited for these highly dynamic topologies since they either rely on centralized servers or on resource-consuming query flooding. Application layer overlays seem to be a more promising approach. However, existing solutions like the ContentAddressable Network (CAN) are especially designed for internet based peerto -peer networks yielding structural conditions that are far too complex for ad hoc networks. Therefore, in this paper, we propose a more lightweight overlay structure: lanes. We present algorithms to correct and optimize its structure in case of topology changes and show how it enables the trading of services specified by arbitrary descriptions.

Peer network systems are becoming an increasingly important development in Web search technology. Many studies show that peer search systems perform better when a query is sent to a group of peers semantically similar to the query. This suggests that semantic communities should form so that a query can quickly propagate to many appropriate peers. For the network to be functional, its dynamic communication topology must match the semantic clustering of peers. We introduce two criteria to evaluate a peer search network based on the concept of semantic locality: first, the “smallworld” topology of the network; second, we use topical semantic similarity to monitor the quality of a peer’s neighbors over time by looking at whether a peer chooses semantically appropriate neighbors to route its queries. We present several simulation experiments conducted with different peer search algorithms on our peer Web search system, 6S. The results suggest that 6S, despite its use of an unstructured overlay network; can effectively foster the spontaneous formation of semantic communities through local peer interactions alone.

In ongoing research, a collaborative peer network application is being proposed to address the scalability limitations of centralized search engines. Here we introduce a local adaptive routing algorithm used to dynamically change the topology of the peer network based on a simple learning scheme driven by query response interactions among neighbors. We test the algorithm via simulations with 70 model users based on actual Web crawls. We find that the network topology rapidly converges from a random network to a small world network, with emerging clusters that match the user communities with shared interests.

Abstract—Peer-to-peer networks are widely criticized for their inefficient flooding search mechanism. Distributed Hash Table (DHT) algorithms have been proposed to improve the search efficiency by mapping the index of a file to a unique peer based on predefined hash functions. However, the tight coupling between indices and hosting peers incurs high maintenance cost in a highly dynamic network. To properly balance the tradeoff between the costs of indexing and searching, we propose the distributed caching and adaptive search (DiCAS) algorithm, where indices are passively cached in a group of peers based on a predefined hash function. Guided by the same function, adaptive search selectively forwards queries to “matched ” peers with a high probability of caching the desired indices. The search cost is reduced due to shrunk searching space. Different from the DHT solutions, distributed caching loosely maps the index of a file to a group of peers in a passive fashion, which saves the cost of updating indices. Our simulation study shows that the DiCAS protocol can significantly reduce the network search traffic with the help of small cache space contributed by each individual peer. Index Terms—Peer-to-peer, query response, flooding, distributed caching and adaptive search, search efficiency. 1

Abstract. The paper describes a design of a peer-to-peer system which is being developed currently to support file and service (help, advise) sharing in research groups and groups of learners. The design addresses some non-technical problems in the deployment of P2P systems, such as coping with free riders, creating closely-knit groups of users sharing common interests and trust. It describes a user modelling approach for servents and presents several approaches for motivating users to participate and contribute to the community. 1.

A collaborative peer network application called 6Search (6S) is proposed to address the scalability limitations of centralized search engines. 6S peers depend on a local adaptive routing algorithm to dynamically change the topology of the peer network and search for the best neighbors to answer their queries. We validate prototypes of the 6S network via simulations with 70 − 500 model users based on actual Web crawls and find that the network topology rapidly converges from a random network to a small world network, with clusters emerging from user communities with shared interests. We finally compare the quality of the results with those obtained by centralized search engines such as Google, suggesting that 6S can draw advantages from the context and coverage of the peer collective.

Peer-to-Peer networks allow users to globally share resources directly with each other. As these users are from all over the world, they will utilize the network differently. For example, they might use their native tongue to describe resources. These differences makes it a difficult task to provide efficient and robust search capabilities within fully distributed P2P networks. In this paper, we show...

Abstract. Distributed Hashtables (DHTs) provide a scalable method of associating file-hashes with a particular location in a distributed network environment. Modifying DHTs directly to support meta-data is difficult, and meta-data search systems such as flooding tend to scale poorly. However, a number of more scalable distributed meta-data search systems have recently been developed that could be deployed in tandem with DHTs, and several are discussed here along with some novel simulation results that concern the scalability and resource limitations of a meta-data search layer that employs semantic routing. Semantic routing is a method of pruning a flooding search such that queries are preferentially forwarded to nodes that can answer those queries. Previous simulations [9] showed that under certain circumstances semantic routing leads to a reduction in search path length. This paper presents further simulation results indicating that the scalability of this effect is a function of the query distribution of individual user search activity. 1.

In this document we provide an overview of the recent approaches in literature on semanticbased service discovery in P2P environment. The deliverable is organized as follows: in Section 1 a description of the main features of P2P and semantic Web service technologies; in Section 2 an overview of the main approaches in literature addressing the problem of designing semantic-enriched P2P systems for service discovery are outlined; Section 3 performs a comparison between the approaches, while in Section 4 we finish with some concluding remarks.