Checking query containment with the CQC method

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.