Semantic Caching for XML Queries

With the advent of XML, great challenges arise from the demand for efficiently retrieving information from remote XML sources across the Internet. The semantic caching technology can help to improve the efficiency of XML query processing in the Web environment. Different from the traditional tuple or page-based caching systems, semantic caching systems exploit the idea of reusing cached query results to answer new queries based on the query containment and rewriting techniques. Fundamental results on the containment of relational queries have been established. In the XML setting, the containment problem remains unexplored for comprehensive XML query languages such as XQuery, and little has been studied with respect to the cache management issue such as replacement. Hence, this dissertation addresses two issues fundamental to building an XQuery-based semantic caching system: XQuery containment and rewriting, and an effective replacement strategy. We first define a restricted XQuery fragment for which the containment problem is tackled. For two given queries Q1 and Q2, a preprocessing step including variable minimization and query normalization is taken to trans-