Efficient Reasoning About XFDs with Pre-image Semantics

The study of integrity constraints has been identified as one of the major challenges in XML database research. The main difficulty is finding a balance between the expressiveness and the existence of automated reasoning tools. We investigate a previous proposal for functional dependencies in XML (XFDs) that is based on homomorphisms between data trees and schema trees. We demonstrate that reasoning about our XFDs is well-founded. We provide a finite axiomatisation and show that their implication is equivalent to the logical implication of propositional Horn clauses and thus decidable in time linear in the size of the constraints. Hence, our XFDs do not only capture valuable semantic information but also permit efficient automated reasoning support.