Re: UniqueProperty, UnambiguousProperty

Hello Ian -

Thanks for the clarification.  Yes, what you say makes sense.  I was worrying
a bit about the fact that UniqueProperty allows one to define a property
without saying whether it's Object or Datatype, which I had assumed one was
not supposed to be able to do.  But I now see that one *is* supposed to be
able to do that.

Best regards,

- David

Ian Horrocks wrote:

> On September 11, David Martin writes:
> > Why is UniqueProperty a subclass of
> >
> >    rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property
> >
> > whereas UnambiguousProperty is a subclass of
> >
> >    #ObjectProperty?
> >
> > This seems especially odd in view of this statement (from the language
> > reference doc): Note that the inverse property of a UniqueProperty is
> > always an UnambigousProperty and vice versa.
> >
> > I sort of thought a design decision had been made that each DAML
> > property should be either Object or Datatype, and that this distinction
> > was supposed to be made clear in its declaration (someone please correct
> > me if I'm wrong).  But, if that's right, UniqueProperty allows one to
> > get around that design decision.
>
> UniqueProperty is just an idiom for a cardinality constraint, and can
> be applied to any property. So, while it is true that each DAML
> property should be either Object or Datatype, instances of both Object
> and Datatype properties can also be instances of UniqueProperty. This
> is why UniqueProperty is a subClass of the more general rdf:Property
> class.
>
> UnambiguousProperty, on the other hand, is basically an idiom for a
> cardinality constraint on the inverse property applied to all objects
> at the "value end" of the property. As only daml objects can be
> instances of such restrictions (i.e., can be instances of daml
> classes), UnambiguousProperty is a subClassOf ObjectProperty.
>
> It is easy to see that these characterisations are consistent with the
> fact that the inverse property of a UniqueProperty is always an
> UnambigousProperty and vice versa.
>
> Regards, Ian
>
> >
> > - David

Received on Tuesday, 11 September 2001 21:12:04 UTC