owl:Restriction and rules

What does an owl:Restriction denote?

[This is about OWL-Full, not OWL-DL.  OWL-DL clearly does not permit named 
restrictions, which are the premis of my initial question.]

Because there are situations in which an owl:Restriction can be used 
interchangeably with a class name (cf. owl:allValuesFrom, 
owl:someValuesFrom) then I think the owl:Restriction node must denote the 
same kind of thing as a named class; i.e. an owl:Class.

In RDF, it would be quite legal to have an rdf:about attribute on an 
owl:Restriction value.  I think that an owl:Restriction with an rdf:about 
attribute may be legal and meaningful in OWL full, since the language guide 
[1] (section 1.1, 3rd bullet) suggests that every legal RDF graph is valid 
in OWL full.

[1] http://www.w3.org/TR/2003/CR-owl-guide-20030818/

It seems to me that following the above, named restrictions would allow one 
to assert that all individuals that satisfy one set of conditions also 
satisfy some other set of conditions, which starts to look a bit like a rule:

    <owl:Restriction rdf:about="#Mortal">
      <owl:onProperty rdf:resource="#lifespan" />
      <owl:hasValue rdf:resource="#finite" />
    </owl:Restriction>

    <owl:Class rdf:about="#Man">
      <rdfs:subClassOf rdf:resource="#Mortal" />
    </owl:Class>

    <owl:Restriction about="#Man" >
      <owl:onProperty rdf:resource="#parent" />
      <owl:minCardinality
        rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality>
    </owl:Restriction>

    <rdf:Description rdf:about="#Socrates" />
      <parent rdf:Resource="#Sophroniscus" />
    </rdf:Description>

Would appear to be sufficient to deduce from the fact that Socrates has a 
parent that he also has a finite lifespan.

My questions to which I'm trying to find answers are:
(a) given named owl:Restrictions, do we really need a separate rules 
language (cf. DAML-rules)?
(b) does OWL-full allow named restrictions?

Digging further, it occurs to me that it does not matter if restrictions 
cannot be labelled.  Isn't the same effect achieved by:

    <owl:Class rdf:about="#Foo"
      <owl:equivalentClass>
        <owl:Restriction>
          :
        </owl:Restriction>
      </owl:equivalentClass>
    </owl:Class>

This suggests to me that the ability of OWL to express rules may be limited 
only by the kinds of conditions that can be used as restrictions.  For 
example, Pan and Horrocks mention a putative <owl:BinaryRestriction> class [2].

[2] http://www.cs.man.ac.uk/~horrocks/Publications/download/2003/PaHo03a.pdf

#g


------------
Graham Klyne
For email:
http://www.ninebynine.org/#Contact

Received on Monday, 3 November 2003 10:56:34 UTC