Nested XPath Query Optimization for XML Structured Document Database

The XPath language is based on a tree representation of the XML document, and provides the ability to navigate around the tree, selecting nodes by a variety of criteria. Here an optimization plan is proposed, to unnest and optimize nested XPath query for XML Inter and Intra document relationship. Inter and Intra document relationships are techniques of implementing one to many relationship. We propose an enhanced variant of kappa join which is used for query unnesting. Further the deterministic optimization approach which exploits the structure of XML document is used to optimize the unnested query. Previous works have focused only on unnesting phase of nested query optimization for a containment and intra document relationship. This paper further extends the unnesting strategy with the deterministic optimization approach for Inter and intra document relationship. The optimization plan starts with unnesting of the query. Unnesting is performed by means of enhanced variant of kappa join taking into account the XML relationship. Unnested query is converted to a internal PAT(Pattern) representation. This PAT expression is optimized by deterministic transformation on queries using the structure knowledge of XML data and structure-related semantics. Then the optimized PAT expression is converted to XPath query. Finally both the normal and optimized query is executed in DB XML database to evaluate the execution time. The final results prove that the optimized query executes faster with better scalability, selectivity and reduction in execution time.