Answering queries posed over knowledge bases is a central problem in knowledge representation and database theory. In databases, query containment is one of the important query optimization and schema integration techniques [1, 12, 16]; in knowledge representation, it has been used for object classification, schema integration, service discovery, and more, in particular in the area of description logics [6, 14]. Results on practical instances of the general problem were studied in [12], followed by [5, 7, 2, 4, 13]. In particular, [5] and [7] deal respectively with query containment and efficient query answering under expressive description logic constraints, that can express several construct used in conceptual data modeling; [2] and [4] address query containment under constraints derived respectively from entity-relationship and object-oriented formalisms. The complexity of reasoning tasks on complex constraints based on answer set programs has been investgated in [19]. The problem ...