Abstract
We consider the network structure and query processing capabilities of social communities like bookmarks and photo sharing communities such as del.icio.us or flickr. A common feature of all these networks is that the content is generated by the users and that users create social links with other users. The evolving network naturally resembles a peer-to-peer system, where the peers correspond to users. We consider the problem of query routing in such a peer-to-peer setting where peers are collaborating to form a distributed search engine. We have identified three query routing paradigms: semantic routing based on query-to-content similarities, social routing based on friendship links within the community, and spiritual routing based on user-to-user similarities such as shared interests or similar behavior. We discuss how these techniques can be integrated into an existing peer-to-peer search engine and present a performance study on search-result quality using real-world data obtained from the social bookmark community del.icio.us.