Answering Tree Pattern Queries Using Views, a revisit

Abstract

We revisit the problem of answering tree pattern queries using views. We first show that, for queries and views that do not have nodes labeled with the wildcard *, there is an alternative to the approach of query rewriting which does not require us to find any rewritings explicitly yet which produces the same answers as the maximal contained rewriting. Then, using the new approach, we give a simple criterion and a corresponding algorithm for identifying redundant view answers, which are view answers that can be ignored when evaluating the maximal contained rewriting. Finally, for queries and views that do have nodes labeled *, we provide a method to find the maximal contained rewriting and show how to answer the query using views without explicitly finding the rewritings.