Re: Asymmetry of Domain and Range in OWL

i agree with chris in not considering this an asymmetry.

I think a main point that we would point out with range is that after a 
range (either global with a range restriction or local with an all 
values from restriction) is used, that description logic reasoners will 
enforce the restriction.  Thus, one could view this that anything that 
is a value of a property with a range restriction will end up being 
"coerced" into being an instance of the range restriction.

we would also want to point out the related issue that if a value 
restriction becomes overconstrained (and thus incoherent), then the 
maximum cardinality restriction ends up getting set to 0 since it is 
impossible for there to be any values of the property.
this does not cause in inconsistency .

deborah

Alan Rector wrote:

> 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 
> <http://www.cs.man.ac.uk/%7Erector/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
>  
>

-- 
 Deborah L. McGuinness 
 Knowledge Systems Laboratory 
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