Optimization of extensible markup language path language (XPATH) expressions in a database management system configured to accept extensible markup language (XML) queries

摘要

An apparatus, system, and method are disclosed for optimization of XPath expressions in a database management system configured to accept XML queries. Operations of the method include receiving an XQuery representation and partitioning XPath expressions within the XQuery representation into a plurality of XPath expression clusters. The XPath expression clusters may comprise one or more XPath expressions and those in each cluster may operate on a common document. Furthermore, the XPath expressions in each cluster are hierarchically related to each other such that branch nodes of the cluster are executable independent of nodes in other XPath expression clusters. The method also defines merging the one or more XPath expressions into one or more expression trees for each XPath expression cluster. The method generates one or more query execution plans from the one or more XPath expression blocks. The method includes, for each query execution plan, splitting each of the XPath expression blocks into one or more ordered fragments. The method determines a cardinality according to database statistics and an execution cost for each XPath expression block within each query execution plan. Finally, the method determines an aggregate cardinality for each query execution plan and an aggregate execution cost for each query execution plan. Therefore, an XQuery may be optimized at both the global XQuery and local XPath expression block level, improving performance and reducing overhead.