Accelerating XPath evaluation in any RDBMS

Abstract

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.

Efficient XML and Entity Retrieval with PF/Tijah: CWI and University of Twente at INEX’08

“…PF/Tijah creates a full-text index on top of Pathfinder's pre/post encoding of XML files [5]. Instead of assigning a pre-order value to complete textnodes as done by the Pathfinder, the Tijah full-text index enumerates each single term.…”

XTRON: An XML data management system using relational databases

“…In general, to process multi-step (k > 1) XPath path expressions, the system generates an SQL query that is nested to depth k, and then this scheme is improved to generate an SQL query involving a k-way self-join [19]. XTRON reduces the number of self-joins using the reverse arithmetic encoding.…”

RDF Querying: Language Constructs and Evaluation Methods Compared

“…This is surprising as these path expressions make query authoring (they allow avoiding recursive views) easier and can be implemented efficiently as research on these constructs for XML query languages has shown. In particular, unrestricted closure path expressions can be implemented nearly as efficiently as basic path expressions using, e.g., tree labeling schemes [48] or closure indices.…”