Finding Equivalent Rewritings with Exact Views

This paper presents a study of equivalent rewritings for conjunctive queries and views: that is, queries and views expressed in terms of database predicates, but not built-in predicates. It analyses conjunctive queries and views with an exact, set semantics, corrects some errors in prior work and shows necessary and sufficient conditions on the query and views for an equivalent rewriting to exist, including showing when a view covers part of a query. The paper presents a sound and complete algorithm for finding equivalent rewritings.