Adding formal semantics to the Web: building on top of RDF Schema.

RDF Schema provides means to define vocabulary, structure and constraints for expressing metadata about Web resources. However, formal semantics for the primitives defined in RDF Schema are not provided, and the expressivity of these primitives is not enough for full-fledged ontological modeling and reasoning. To perform these tasks, an additional layer on top of RDF Schema is needed. In this paper, we will show how RDF Schema can be extended in such a way that a full knowledge representation language can be expressed in it, thus enriching it with the required additional expressivity and the semantics of this language. We do this by describing the ontology language OIL as an extension of RDF Schema. First, we give a short introduction to both RDF Schema and OIL. We then proceed to define a Schema to express OIL ontologies in RDF, where the aim is to use existing RDF terminology where possible, and extending RDF(S) where necessary. The result is an RDF Schema definition of OIL primitives, which allows one to express any OIL ontology in RDF syntax, thus enabling the added benefits of OIL, such as reasoning support and formal semantics, to be used on the Web. We conclude that our method of extending is equally applicable to other knowledge representation formalisms.