FullDifferencesSpecIntro

Discussion of the introductory parts of the OWL-Full spec.

The following text is copied&pasted from the OWL-Full spec.

The introduction of the OWL-Full spec

5. RDF-Compatible Model-Theoretic Semantics (Normative)
=======================================================

This model-theoretic semantics for OWL is an extension 
of the semantics defined in the RDF semantics [RDF Semantics], 
and defines the OWL semantic extension of RDF.

NOTE: There is a strong correspondence between 
the semantics for OWL DL defined in this section 
and the Direct Model-Theoretic Semantics defined in Section 3 
(see Theorem 1 and Theorem 2 in Section 5.4). 
If, however, any conflict should ever arise 
between these two forms, then the Direct Model-Theoretic Semantics 
takes precedence.

The first section of the OWL-Full spec

5.1. The OWL and RDF universes
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All of the OWL vocabulary is defined on the 'OWL universe', 
which is a division of part of the RDF universe into three parts, 
namely OWL individuals, classes, and properties. 
The class extension of owl:Thing comprises the individuals 
of the OWL universe. The class extension of owl:Class 
comprises the classes of the OWL universe. 

The union of the class extensions of 
owl:ObjectProperty, owl:DatatypeProperty, owl:AnnotationProperty, 
and owl:OntologyProperty comprises the properties of the OWL universe.

There are two different styles of using OWL.

In the more free-wheeling style, called OWL Full, 
the three parts of the OWL universe are identified 
with their RDF counterparts, namely the class extensions 
of rdfs:Resource, rdfs:Class, and rdf:Property. 
In OWL Full, as in RDF, elements of the OWL universe 
can be both an individual and a class, 
or, in fact, even an individual, a class, and a property. 

In the more restrictive style, called OWL DL here, 
the three parts are different from their RDF counterparts 
and, moreover, pairwise disjoint. 
The more-restrictive OWL DL style gives up some expressive power 
in return for decidability of entailment.

Both styles of OWL provide entailments that are missing 
in a naive translation of the DAML+OIL model-theoretic semantics 
into the RDF semantics.

A major difference in practice between the two styles 
lies in the care that is required to ensure that URI references 
are actually in the appropriate part of the OWL universe. 
In OWL Full, no care is needed. In OWL DL, localizing information 
must be provided for many of the URI references used. 
These localizing assumptions are all trivially true in OWL Full, 
and can also be ignored when one uses the OWL abstract syntax, 
which corresponds closely to OWL DL. But when writing OWL DL in triples, 
however, close attention must be paid to which elements 
of the vocabulary belong to which part of the OWL universe.

Throughout this section the OWL vocabulary will be 
the disallowed vocabulary from OWL plus the built-in classes, 
the built-in annotation properties, and the built-in ontology properties.