System and method for query processing and optimization for XML repositories

摘要

A computer program product is provided as a system for querying a repository of XML documents. The data in the XML documents are viewed by a query system as a graph that allows queries on content, structure, inter-document links, and intra-document links. The query language uses XML syntax and is based on tree pattern match semantics. The features of the query language allow the query system to compute a DTD for the query language and to use it to validate the user query formulation. Query optimization is done using schema-based optimization and index based optimization. Optimization uses the schema for (a) minimizing the number of documents on which the query need to be executed; (b) eliminating redundant conditions specified in the query; and (c) simplifying expensive query constructs. The query system maintains three sets of indices for each XML document: (a) value indices corresponding to text; (b) structure indices corresponding to tree structure patterns; and (c) link indices corresponding to link relationships.