New Rewritings and Optimizations for Regular Path Queries

Abstract

All the languages for querying semistructured data and the web use as an integral part regular expressions. Based on practical observations, finding the paths that satisfy those regular expressions is very expensive. In this paper, we introduce the “maximal partial rewritings” (MPR’s) for regular path queries using views. The MPR’s are always exact and more useful for the optimization of the regular path queries than other rewritings from previously known methods. We develop an algorithm for computing MPR’s and prove, through a complexity theoretic analysis, that our algorithm is essentially optimal. Also, we present query answering algorithms that utilize exact partial rewritings for regular path queries and conjunctive regular path queries respectively.