rigoris Antoniou and Frank van Harmelen rdfs Resource rdfs: Class rdf: Property owl Class owl: Object Propert Fig. 1. Subclass relationships between OWL and RDF/RDFS The original hope in the design of owl was that there would be a down- ward compatibility with corresponding re-use of software across the various layers. However, the advantage of full downward compatibility for OWL(that any OWl aware processor will also provide correct interpretations of any RDF Schema document) is only achieved for OWL Full, at the cost of computa tional intractability Chapter overview Section 2 presents OWL in some detail. Because OWL is such a new language, only very limited examples of its use have been published. Section 3 therefore lustrates the lang 2 The OWL Lang OWL builds on RDF and RDF Schema, and uses RDF's XML syntax. Since this is the primary syntax for OWL, we will use it here, but it will soon become clear that RDF/XML does not provide a very readable syntax. Because of this other syntactic forms for Owl have also been defined an XML-based syntax which does not follow the RDF conventions. This makes this syntax already significantly easier to read by humans an abstract syntax which is used in the language specification document This syntax is much more compact and readable then either the XML syntax or the RDF/XML synta a graphical syntax based on the conventions of the UML language(Uni- versal Modelling Language). Since UML is widely used, this will be an easy way for people to get familiar with OWL6 Grigoris Antoniou and Frank van Harmelen rdfs:Class owl:Class owl:ObjectProperty owl:DatatypeProperty rdf:Property rdfs:Resource Fig. 1. Subclass relationships between OWL and RDF/RDFS The original hope in the design of OWL was that there would be a down￾ward compatibility with corresponding re-use of software across the various layers. However, the advantage of full downward compatibility for OWL (that any OWL aware processor will also provide correct interpretations of any RDF Schema document) is only achieved for OWL Full, at the cost of computa￾tional intractability. Chapter overview Section 2 presents OWL in some detail. Because OWL is such a new language, only very limited examples of its use have been published. Section 3 therefore illustrates the language by giving a few examples. 2 The OWL Language Syntax OWL builds on RDF and RDF Schema, and uses RDF’s XML syntax. Since this is the primary syntax for OWL, we will use it here, but it will soon become clear that RDF/XML does not provide a very readable syntax. Because of this, other syntactic forms for OWL have also been defined: • an XML-based syntax which does not follow the RDF conventions. This makes this syntax already significantly easier to read by humans. • an abstract syntax which is used in the language specification document. This syntax is much more compact and readable then either the XML syntax or the RDF/XML syntax • a graphical syntax based on the conventions of the UML language (Uni￾versal Modelling Language). Since UML is widely used, this will be an easy way for people to get familiar with OWL