Extending OWL with Explicit Dependency

Functional Dependency has been extensively studied in database theory. It provides an elegant formalism for specifying key constraints and is the basis for normalization theory used in Relational database design. Given its known axiomatization through logical implications it is expected that the ontology community would be interested in investigating its applicability to conceptual modeling. This paper investigates the extension of OWL ontologies with functional dependencies. In particular, we focus on key dependency and a new class referred to as explicit dependency. The latter is a functional dependency in which the function that correlates the left-hand side to the right-hand side of the dependency is known. We extend current formalism to allow functions to appear in the consequent of a dependency declaration. A mapping of the proposed formalism to Horn clause is specified and permits FDs to be evaluated as logic rules. The ontology therein produced may present different behaviors depending on the interpretation given to functional dependencies. Interesting enough is that explicit dependency adds one extra possible interpretation, similar to views in databases. We have integrated the extended formalism into OWL and used SWRL to map dependencies to logic rules. A prototype has been implemented and illustrates the proposed approach.