Contained Rewritings of XPath Queries Using Views Revisited

Abstract

We revisit the problem of finding maximal contained rewritings of tree pattern queries using views, and extend previous work to the case where both the query and the view involve *, with the restriction that no *-node is incident on any //-edge, and there are no leaf *-nodes. When there is no dtd, we show how to modify the approach of useful embedding in a previous work to find the maximal contained rewriting. When there is a dtd that is represented as an acyclic schema graph G, we show how to efficiently transform the view V to an equivalent DAG-pattern V′, and reduce the problem of finding the maximal contained rewriting of query Q using V under G to that of finding the maximal contained rewriting of Q using V′ without dtds.