Asymmetry of Domain and Range in OWL

Pat, All

Sorry for not giving a clear explanation last night.  There are slides (as soon as our server comes back)
at www.cs.man.ac.uk/~rector/papers/common-errors-ekaw.html.  The slides (available in both pdf and .ppt) have the clearest explanation of the point - towards the end.

I summarise in N3 notation below..

Supposed I have a property

:has_topping
      a       owl:ObjectProperty ;
      rdfs:domain :Pizza ;
      rdfs:range :Pizza_topping .


And classes
:Pizza
      a       owl:Class .
:Pizza_topping
      a       owl:Class .
:Ice_cream
      a       owl:Class .
:Ice_cream_cone
      a       owl:Class ;


And I add an existential restriction that 'violates' both the domain and range restrictions, say

:Ice_cream_cone
      rdfs:subClassOf
              [ a       owl:Restriction ;
                owl:onProperty :has_topping ;
                owl:someValuesFrom :Ice_cream
              ] .

If there are no disjoint axioms, then what happens is that Ice_cream_cone is classified as a kind of Pizza, and is satisfiable. The 'violation' of the range restriction is ignored.

If there are disjoint axioms, then Ice_cream_cone is unsatisfiable if either the domain or range constraint is violated, but there is no effect on Ice_cream, because the statement is about 'some Ice_cream' rather than 'All Ice_cream'.

New users find  confusing the fact that 'violation' of domain constraints can cause things to be reclassified (programmers tend to call it 'coerced') but range constraints cannot. (except if the inverse property is used, in which the domain and range swap roles)

I put  'violation' in scare quotes because, of course. without the disjoint axioms, it isn't really a violation according to OWL semantics, but it is almost certainly an error in the sense of not being what the user intended.

Regards

Alan






  --
Alan L Rector
Professor of Medical Informatics
Department of Computer Science
University of Manchester
Manchester M13 9PL, UK
TEL: +44-161-275-6188/6149/7183
FAX: +44-161-275-6236/6204
Room: 2.88a, Kilburn Building
email: rector@cs.man.ac.uk
web: www.cs.man.ac.uk/mig
        www.opengalen.org
        www.clinical-escience.org
        www.co-ode.org