Introduction

XQP is a dynamic and scalable architecture for indexing and querying a large distributed repository of schema-less XML data, implemented on top of a structured peer-to-peer (P2P) system (Pastry). Unlike other approaches, XQP can process most forms of XQuery extended with full-text search, even those queries that search for multiple documents that are related through join conditions. The indexing is based on both the text terms and the structural summary of a document. Given an XQuery, our system can find all the plausible structural summaries applicable to the query using one peer lookup only. Each structural summary is associated with a small, dynamically adapting sub-space of peers who share the inverted lists related to all the documents that conform to this particular structural summary. Peers may participate in multiple sub-spaces, while the size of each sub-space may grow and shrink dynamically, depending on the workload. To locate multiple documents that are related through join conditions, XQP uses value histograms distributed over the P2P network.

XQP architecture



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