Determinacy and rewriting of conjunctive queries over unary database schemas
Lixiao Zheng, Haiming Chen · 2011
The problem of answering queries using views arises in a wide variety of data management applications. From the information-theoretic perspective, a notion of determinacy has been recently introduced to formalize the intuitive notion that whether a set of views V is sufficient to answer a query Q. We say that V determines Q iff for any two databases D1, D2, V(D1) = V(D2) implies Q(D1) = Q(D2). Determinacy has been investigated for many query and view languages including first order logic (FO) and unions of conjunctive queries (UCQ) and a considerable number of cases are resolved. However the problem remains open for queries and views defined by conjunctive queries (CQ) and appears to be quite challenging.