XPCache: An Efficient Query Processor for Client-Server Architecture

This study addresses the problem of distributed XML queries in client-server architecture. Distributed XML documents can be large and complex. Due to the overhead involved in decomposing the queries, sending the decomposed queries to remote site(s), and executing structural join operations to compose the results, it can be difficult to rapidly execute queries on these distributed XML docs. We propose a query processor called XPCache to tackle those problems. We describe a Global Query Graph, a novel mechanism used by XPCache to classify queries based on their type and frequency. We then describe XPCache´s mechanisms that exploit those classifications to improve query response time. Queries classified under the same type are given the same query optimization plan. These plans are cached at the central site. Queries classified as frequently used are answered from the central site cache, which improves query response time. The performance of XPCache is compared with another system and the results showing marked performance improvement.