Coordination points between RDF(S) and DAML+OIL.

• what does DAML+OIL depend on from RDF(S)
• RDF triple structure
• RDF Schema constructions
• what does DAML+OIL not use at all
• reification
• containers
• meta-classes
• what changes does DAML+OIL require in RDF(S)
• multiple domains with intersection semantics
• multiple ranges with intersection semantics
• cycles in subclass- and subproperty-hierarchies
• what areas of RDF(S) problematic
• syntax
• normalisation
• datatypes
• scoping
• layering
• Syntax of URIs:
• Semantics of URIs:

• DAML+OIL builds on the basic triple-structure provided by RDF. In its essence all that DAML+OIL does is to assign a specific interpretation to certain designated RDF triples (see the corresponding remarks in the DAML+OIL reference document and in the model theoretic semantics of DAML+OIL.
• Some of these designated triples are inherited from RDF Schema. DAML+OIL assigns a semantics for these triples which we believe was also the intended semantics of these triples in the RDF Schema definition. We use RDF Schema classes, the class hierarchy organisation, and the structuring of properties: rdf:type, rdfs:class, rdf:value, rdfs:subClassOf, rdfs:subPropertyOf, rdfs:domain and rdfs:range.

• Reification of statements: The reason for this is twofold. Firstly, no such language construct was felt necessary for a basic ontology infrastructure language, and secondly the semantics of the RDF Schema construction is poorly understood.
• Containers: Although a notion of containers is required in DAML+OIL (in particular sets), the containers as provided by RDF have the wrong properties to be useful for us. An important property of containers in RDF (whether by accident or by design) is that they cannot be "closed". External sources can always make additional statements the contents of a container, effectively "adding" elements. In DAML+OIL, it is crucial to be able to state that a container contains exactly the indicated arguments, and >*no more*<. This is important in for instance the "disjointUnionOf statement". Such a "closure condition" on containers is impossible (or at least very hard) to express using RDF containers.
• RDFS - meta-class organization: With meta-classes in this context we mean classes that have other classes as their members. RDF Schema allows such meta-classes (see e.g. the explanation on rdf:type in the RDF Schema recommendation). DAML+OIL allows only instances to be members of classes. Classes can be a subclasses of other classes, but never members. I.e. DAML+OIL does not contain meta-classes. To be sure, as part of a DAML+OIL document, one can write a statement making one class an instance of another class, but such a statement is not assigned any DAML+OIL semantics.
  Although meta-classes are therefore not available to users of DAML+OIL (in the sense described above, namely that DAML+OIL provides no semantics for it), meta-classes in RDF Schema have been used by the designers of DAML+OIL to define DAML+OIL in terms of RDF Schema. For example, the RDF Schema definition of DAML+OIL starts with the definition of two meta-classes, namely the class of object-classes and the class of all datatype classes.
  Summarising:
  • meta-classes are classes with other classes as members
  • RDF Schema allows such meta-classes
  • such meta-classes are not given any semantics under DAML+OIL
  • the RDF Schema definition of DAML+OIL does exploit such meta-classes.