A utilization of schema constraints to transform predicates in XPath query

Abstract

A predicate in an XPath query expresses a condition to be fulfilled in addition to the structural constraint imposed by the path itself. The condition is a Boolean expression. It may involve comparisons between elements and values, path expressions denoting elements to be compared as well as further path expressions. In this paper, we are concerned with the semantic transformation of such predicates in the presence of a schema for the XML data. The goal of this semantic transformation is to eliminate the predicates from the XPath query if possible in order to avoid the early, unnecessary query processing. Otherwise, if predicates are retained, we show how they can be semantically transformed to boost efficiency and reduce resource utilization. An algorithm is proposed to determine whether predicates should be eliminated or retained. We implement the proposed transformations and empirically evaluate their efficiency and effectiveness as semantic query optimization devices. © 2010 Springer-Verlag.