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[protege-owl] Transitivity isn't working!! Why?
tar at isi.edu
Wed Nov 3 11:02:10 PDT 2010
On Nov 3, 2010, at 7:23 AM, Bram Gadeyne wrote:
> Hi all,
> I'm also using the transitivity relation with protege owl 3.4.
> But the log of Pellet indicates that it ignores the transitivity
> relation because of a cardinality restriction on the object property.
> I did not indicate this restriction in with the property itself. The
> only things I can find are within the necessary and sufficient blok
> of some classes where I state the following:
> 1) isPeriodPartOf only abstract_period (with isPeriodPartOf beiing
> defined as a transitive property.)
> 2) hasPeriodParts min 2 (with hasPeriodParts beiing the inverse of
> isPeriodPartOf and also transitive.)
> But I would think that such a restriction in a necessary and
> sufficient block would not generate such a warning in pellet since
> it is not a global cardinality restriction.
This violates the Structural Specification of OWL 2:
"transitive properties cannot be used in number restrictions"
Only simple properties can be used in number restrictions (and in some
other constructs). This is required to make sure that the
classification problem is decidable.
Pellet's behavior is presumably due to a desire to try to work with
the ontology by ignoring the axioms that violate the OWL 2 DL
restrictions in order to process the widest possible set of
ontologies. The other alternative would be to reject the ontology for
reasoning completely. So I think the Pellet designers chose a more
practically useful approach. I suppose one could debate whether to
drop transitivity or cardinality restrictions, but one of them needs
to go in order to satisfy the requirements of OWL 2 DL.
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