An optimization technique for answering regular path queries

Abstract

Rewriting queries using views is a powerful technique that has applications in data integration, data warehousing and query optimization. Query rewriting in relational databases is by now rather well investigated. However, in the framework of semistructured data the problem of rewriting has received much less attention. In this paper we identify some diffculties with currently known methods for using rewritings in semistructured databases. We study the problem in a realistic setting, proposed in information integration systems such as the Information Manifold, in which the data sources are modelled as sound views overa global schema. We give a new rewriting, which we call the possibility rewriting, that can be used in pruning the search space when answering queries using views. The possibility rewriting can be computed in time polynomial in the size of the original query and the view definitions. Finally, we show by means of a realistic example that our method canreduce the search space by an order of magnitude. © Springer-Verlag Berlin Heidelberg 2001.