A general procedure to check conjunctive query containment

Abstract. In this paper, we present a general procedure to test conjunctive query containment. We divide the containment problem into four categories, taking into account the underlying semantics (set or bag theoretic) and the presence or absence of built-in predicates in the queries.After a brief review of previous work on conjunctive query containment, we present a new procedure, called QCC (Query Containment Checker), which we show to be a general and uniform procedure to check the containment among conjunctive queries under the four categories mentioned above. We briefly describe the use of QCC to check bag containment of conjunctive queries, and explain in detail how to use QCC to check set containment of conjunctive queries with built-in predicates. In our conclusions, we point out some uses of QCC for other types of containment.