Taming XPath Queries by MinimizingWildcard Steps

Overview

This paper presents a novel and complementary technique to optimize an XPath query by minimizing its wildcard steps. The approach is based on using a general composite axis called the layer axis, to rewrite a sequence of XPath steps (all of which are wildcard steps except for possibly the last) into a single layer-axis step. The paper describes an efficient implementation of the layer axis and presents a novel and efficient rewriting algorithm to minimize both non-branching as well as branching wildcard steps in XPath queries. It also demonstrates the usefulness of wildcard-step elimination by proposing an optimized evaluation strategy for wildcard-free XPath queries that enables selective loading of only the relevant input XML data for query evaluation.