Checking query containment with the CQC method

摘要

We present the Constructive Query Containment (CQC) method to check query containment and query containment under constraints for queries over databases with safe negation in both IDB and EDB subgoals and with or without built-in predicates. The aim of the CQC method is to construct a counterexample that proves that the query containment relationship being checked does not hold. The method uses different Variable Instantiation Patterns (VIPs) to generate only relevant counterexamples according to the syntactic properties of the queries and the databases considered in each test.The main contribution of the CQC method is threefold: it handles broader cases of queries and database schemas than most previous methods, it checks “true” containment instead of uniform containment (which is a sufficient but not necessary condition for containment) and it is not less efficient than other methods for the cases that they handle. Moreover, we prove also soundness and completeness of our method both for success and for failure.