Schema-assisted peer selection for XML querying in unstructured P2P systems

XML is emerging as the de-facto standard for semistructured contents and metadata. Searching this content in mobile environments is challenging, since centralized approaches are not appropriate in a very dynamic environment with limited resources available for keeping a centralized index up-to-date. A more appropriate solution is to organize the mobile devices in an unstructured peerto- peer (P2P) network. The main challenge in the context of unstructured P2P is to determine the peers that might store documents matching a query, i.e., peer selection. In this paper, we propose a summary caching method for increasing the efficiency and recall of peer selection during XML querying. Our approach is based on caching parts of XML schemas along the query path, to enable subsequent jumps to remote peers storing content relevant to the query. We evaluate the performance improvements of our search strategy in terms of completeness of the search and reduced latency. The results show that our approach can significantly enhance a naive query mechanism such as flooding, and consistently outperform a baseline path caching technique similar to techniques used in related work.