This work is a proposal for a database index structure that has been specifically designed to support the evaluation of XPath queries. As such, the index is capable to support all XPath axes (including ancestor, following, precedingsibling, descendant-or-self, etc.). This feature lets the index stand out among related work on XML indexing structures which had a focus on regular path expressions (which correspond to the XPath axes children and descendantor-self plus name tests). Its ability to start traversals from arbitrary context nodes in an XML document additionally enables the index to support the evaluation of path traversals embedded in XQuery expressions. Despite its flexibility, the new index can be implemented and queried using purely relational techniques, but it performs especially well if the underlying database host provides support for R-trees. A performance assessment which shows quite promising results completes this proposal.

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This article is a proposal for a database index structure, the XPath accelerator, that has been specifically designed to support the evaluation of XPath path expressions. As such, the index is capable to support all XPath axes (including ancestor, following, preceding-sibling, descendant-or-self, etc.). This feature lets the index stand out among related work on XML indexing structures which had a focus on the child and descendant axes only. The index has been designed with a close eye on the XPath semantics as well as the desire to engineer its internals so that it can be supported well by existing relational database query processing technology: the index (a) permits set-oriented (or, rather, sequence-oriented) path evaluation, and (b) can be implemented and queried using well-established relational index structures, notably B-trees and R-trees.We discuss the implementation of the XPath accelerator on top of different database backends and show that the index performs well on all levels of the memory hierarchy, including disk-based and main-memory based database systems.

This work is a proposal for a database index structure that has been specifically designed to support the evaluation of XPath queries. As such, the index is capable to support all XPath axes (including ancestor, following, precedingsibling, descendant-or-self, etc.). This feature lets the index stand out among related work on XML indexing structures which had a focus on regular path expressions (which correspond to the XPath axes children and descendantor-self plus name tests). Its ability to start traversals from arbitrary context nodes in an XML document additionally enables the index to support the evaluation of path traversals embedded in XQuery expressions. Despite its flexibility, the new index can be implemented and queried using purely relational techniques, but it performs especially well if the underlying database host provides support for R-trees. A performance assessment which shows quite promising results completes this proposal.

No abstract