Web Ontology Language: OWL Grigoris Antoniou and Frank van Harmelen Department of Computer Science, University of Crete, ga@csduocgr Department of Al, Vrije Universiteit Amsterdam Frank, van Harmelen@cs. vu, nl 1 Motivation and overview The expressivity of RDF and RDF Schema that was described in [12 is de- liberately very limited: RDF is(roughly) limited to binary ground predicates and RDF Schema is(again roughly) limited to a subclass hierarchy and a property hierarchy, with domain and range definitions of these properties However, the Web Ontology Working Group of W3C3 identified of characteristic use-cases for Ontologies on the Web which would require much more expressiveness than RDF and RDF Schema A number of research groups in both America and Europe had already identified the need for a more powerful ontology modelling language. This lead to a joint initiative to define a richer language, called DAML+oiL(the name is the join of the names of the American proposal DAML-ont, and the European language OIL) DAML+OIL in turn was taken as the starting point for the W3C Web Ontology Working Group in defining OWL, the language that is aimed to be the standardised and broadly accepted ontology language of the Semantic In this chapter, we first describe the motivation for OWL in terms of its requirements, and the resulting non-trivial relation with RDF Schema. We then describe the various language elements of OWL in some deta Ontology languages allow users to write explicit, formal conceptualizations of domains models. The main requirements are 3http://www.w3.org/2001/sw/webont http://www.daml.org/2001/03/daml+oil-index.html http://www.daml.org/2000/10/daml-ont.html http://www.ontoknowledge.org/Web Ontology Language: OWL Grigoris Antoniou1 and Frank van Harmelen2 1 Department of Computer Science, University of Crete, ga@csd.uoc.gr 2 Department of AI, Vrije Universiteit Amsterdam, Frank.van.Harmelen@cs.vu.nl 1 Motivation and Overview The expressivity of RDF and RDF Schema that was described in [12] is de￾liberately very limited: RDF is (roughly) limited to binary ground predicates, and RDF Schema is (again roughly) limited to a subclass hierarchy and a property hierarchy, with domain and range definitions of these properties. However, the Web Ontology Working Group of W3C3 identified a number of characteristic use-cases for Ontologies on the Web which would require much more expressiveness than RDF and RDF Schema. A number of research groups in both America and Europe had already identified the need for a more powerful ontology modelling language. This lead to a joint initiative to define a richer language, called DAML+OIL4 (the name is the join of the names of the American proposal DAML-ONT5 , and the European language OIL6 ). DAML+OIL in turn was taken as the starting point for the W3C Web Ontology Working Group in defining OWL, the language that is aimed to be the standardised and broadly accepted ontology language of the Semantic Web. In this chapter, we first describe the motivation for OWL in terms of its requirements, and the resulting non-trivial relation with RDF Schema. We then describe the various language elements of OWL in some detail. Requirements for ontology languages Ontology languages allow users to write explicit, formal conceptualizations of domains models. The main requirements are: 3 http://www.w3.org/2001/sw/WebOnt/ 4 http://www.daml.org/2001/03/daml+oil-index.html 5 http://www.daml.org/2000/10/daml-ont.html 6 http://www.ontoknowledge.org/oil/