[foaf-dev] Funky OWL-stuff with FOAF groups

Hi Dan,

Here's an attempt to explain the trick with FOAF groups we talked about at the Benelux semweb meetup yesterday.

Suppose I define a new group called :agroup as follows:

:agroup rdf:type owl:Class ,
                 owl:NamedIndividual ;
        owl:equivalentClass [ rdf:type owl:Restriction ;
                              owl:onProperty [ owl:inverseOf <http://xmlns.com/foaf/0.1/member>
                                             ] ;
                              owl:hasValue :agroup
                            ] ;
        rdfs:subClassOf <http://xmlns.com/foaf/0.1/Group> .

What I say here is that it is both a subclass of foaf:Group *and* a named individual. Membership of the class can be inferred if the named individual has a foaf:member relation with some resource. OWL 2 DL reasoners won't complain because this is just punning.

The trick works both ways: instances will become foaf:members, and foaf:members will become instances.

Attached is an example ontology with four individuals: there's :agroup, two instances of :agroup (:dan and :rinke) and a foaf:Person called :guus who is asserted to be a foaf:member of :agroup.

Running a reasoner will infer:

:agroup foaf:member :dan, :rinke .
:guus   a           :agroup .

From a purist point of view this is butt-ugly (if :guus is an instance of :agroup, then :guus should be a group), but ... it works.

Note: you can't generalise this for all groups, i.e. there is no way to specify that every member of a subclass must have a relation to that subclass-as-individual.

Cheers,

Rinke



---
Dr Rinke Hoekstra

AI Department         |   Leibniz Center for Law    
Faculty of Sciences   |   Faculty of Law            
Vrije Universiteit    |   Universiteit van Amsterdam
De Boelelaan 1081a    |   Kloveniersburgwal 48      
1081 HV Amsterdam     |   1012 CX  Amsterdam        
+31-(0)20-5987752     |   +31-(0)20-5253497         
hoekstra-vHs5IaWfoDhmR6Xm/[email protected]    |   hoekstra-V/Xpf/[email protected]           

Homepage: http://www.few.vu.nl/~hoekstra

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