More Functional Dependencies for XML

Abstract

In this paper, we present a new approach towards functional dependencies in XML documents based on homomorphisms between XML data trees and XML schema graphs. While this approach allows us to capture functional dependencies similar to those recently studied by Arenas/Libkin and by Lee/Ling/Low, it also gives rise to a further class of functional dependencies in XML documents. We address some essential differences between the two classes of functional dependencies under discussion resulting in different expressiveness and different inference rules. Examples demonstrate that both classes of functional dependencies appear quite naturally in practice and, thus, should be taken into consideration when designing XML documents.