Complete and Equivalent Query Rewriting Using Views

Abstract

Query rewriting using views is a technique for answering a query that exploits a set of views instead of accessing the database relations directly. There are two categories of rewritings, i.e., equivalent rewritings using materialized views applied in query optimization, and maximally contained rewritings used mainly in data integration. Although maximally contained rewritings are acceptable in data integration, there are cases where an equivalent rewriting is desired. More importantly, the maximally contained rewriting is a union of contained queries, many of which are redundant. This paper gives an efficient algorithm to find a complete and equivalent rewriting that is a single conjunctive query. We prove that the algorithm is guaranteed to find all the complete and equivalent rewritings, and that the resulting rewriting is guaranteed to be an equivalent one without additional containment checking. We also show that our algorithm is much faster than others through complexity analysis and experimentation.