domain/range for skos props

Hi Benjamin,

> Imagine the nice search apps, that could then tell us "sorry, 
> I couldn't
> find any [images] from [semantic web conferences], but would 
> you perhaps
> be interested in [videos] from [rdf workshops]?"
> ...the reasoner developers will surely hate you.. ;)

Nice comment :)

> Haven't thought about the other ones (broader, narrower, etc), but if
> broadening their domain/range doesn't raise any problems with the skos
> semantics, I can see a lot of utility in mixing "hard" 
> owl/rdfs relations
> with "softer" skos relations and using the result as an 
> integrated model.

This opens up a very interesting area of discussion.

Currently, SKOS Core has the following structure (inherited from the
original LIMBER RDF schema which was the ancestor of SKOS Core):

skos:semanticRelation  a  rdf:Property;
  rdfs:domain  skos:Concept;
  rdfs:range   skos:Concept.

skos:broader  a  rdf:Property;
  rdfs:subPropertyOf  skos:semanticRelation.

skos:narrower  a  rdf:Property;
  rdfs:subPropertyOf  skos:semanticRelation.

skos:related  a  rdf:Property;
  rdfs:subPropertyOf  skos:semanticRelation.

What this means is that there are no explicit *constraints* on the way
skos:broader/narrower/related are used.  

What it means also is that an RDFS inference engine, given the following
data:

ex:A  skos:broader  ex:B.

... will firstly infer (from sub-property statement) ...

ex:A  skos:semanticRelation  ex:B.

... and then will infer (from domain/range statements) ...

ex:A  a  skos:Concept.
ex:B  a  skos:Concept.

One question I have is: what is the value of this behaviour?

Relating back to Benjamin's initial point: if we decide that
skos:broader/narrower/related should only be used with skos:Concepts, then
this behaviour seems appropriate; however if we decide that it's OK to use
skos:broader/narrower/related with any type of resource, then this behaviour
seems inappropriate (??).

An alternative would be to remove domain/range statements on
skos:semanticRelation, but to introduce OWL restrictions on the skos:Concept
class, e.g.

<rdfs:Class rdf:about="#Concept">
  <rdfs:subClassOf>
    <owl:Restriction>
      <owl:onProperty rdf:resource="#broader" />
      <owl:allValuesFrom rdf:resource="#Concept" />      
    </owl:Restriction>
  </rdfs:subClassOf
</rdfs:Class>

This means that skos:broader/narrower/related could be used with any type of
resource, but when used on a skos:Concept must point to another
skos:Concept.  (Is this the type of constraint we want?)

Another idea I wanted to air for comment is the following:

 - Add a new class skos:SemanticRelationProperty (sub-class of rdf:Property)
 - Add a new class skos:SemanticRelationStatement (sub-class of
rdf:Statement)
 - (And possibly drop skos:semanticRelation, although not sure about that)

The main reason for this is to support RDF descriptions of explicit scheme
membership of semantic relationships (a requirement that has come to me from
several sources).

The new vocab above could have the following constraints:

<rdfs:Class rdf:about="#SemanticRelationStatement">
  <rdfs:subClassOf rdf:resource="&rdf;Statement"/>
  <rdfs:subClassOf>
    <owl:Restriction>
      <owl:onProperty rdf:resource="&rdf;subject" />
      <owl:allValuesFrom rdf:resource="#Concept" />      
    </owl:Restriction>    
  </rdfs:subClassOf>
  <rdfs:subClassOf>
    <owl:Restriction>
      <owl:onProperty rdf:resource="&rdf;predicate" />
      <owl:allValuesFrom rdf:resource="#SemanticRelationProperty" />      
    </owl:Restriction>    
  </rdfs:subClassOf>
  <rdfs:subClassOf>
    <owl:Restriction>
      <owl:onProperty rdf:resource="&rdf;object" />
      <owl:allValuesFrom rdf:resource="#Concept" />      
    </owl:Restriction>    
  </rdfs:subClassOf>
  <rdfs:subClassOf>
    <owl:Restriction>
      <owl:onProperty rdf:resource="#inScheme" />
      <owl:allValuesFrom rdf:resource="#ConceptScheme" />      
    </owl:Restriction>    
  </rdfs:subClassOf>
</rdfs:Class>

... allowing validation of statements like:

<skos:SemanticRelationStatement>
  <rdf:subject rdf:resource="http://foo.com/#foobar"/>
  <rdf:predicate rdf:resource="&skos;broader"/>
  <rdf:object rdf:resource="http://foo.com/#bar"/>
  <skos:inScheme rdf:resource="http://foo.com/scheme"/>
</skos:SemanticRelationStatement>

All food for thought :)

Al.



> 
> 
> benjamin
> 
> --
> Benjamin Nowack
> 
> Kruppstr. 100
> 45145 Essen, Germany
> http://www.appmosphere.com/
> 
> 
> >
> >N.B. skos:prefLabel and skos:altLabel have no domain 
> statement for exactly
> >this reason.
> >
> >Al.
> >
> >---
> >Alistair Miles
> >Research Associate
> >CCLRC - Rutherford Appleton Laboratory
> >Building R1 Room 1.60
> >Fermi Avenue
> >Chilton
> >Didcot
> >Oxfordshire OX11 0QX
> >United Kingdom
> >Email:        a.j.miles@rl.ac.uk
> >Tel: +44 (0)1235 445440
> >
> >
> >
> 
>

Received on Thursday, 21 October 2004 12:02:30 UTC