Boolean operations and inclusion test for attribute–element constraints

The history of schema languages for XML is (roughly) an increase of expressiveness. While early schema languages mainly focused on the element structure, Clark first paid an equal attention to attributes by allowing both element and attribute constraints in a single constraint expression (we call his mechanism “attribute–element constraints”). In this paper, we investigate intersection and difference operations and inclusion test for attribute–element constraints, in view of their importance in static typechecking for XML processing programs. The contributions here are (1) proofs of closure under intersection and difference as well as decidability of inclusion test and (2) algorithm formulations incorporating a “divide-and-conquer” strategy for avoiding an exponential blow-up for typical inputs.