[Pellet-users] Check for no subclass

[Bijan Parsia]

On Feb 24, 2008, at 1:55 PM, Alexander Musidlowski wrote:

> Hi,
>
> i think you refer to the sentence "and owl:Nothing is a subclass of
> every class". As EquivalentClass is a SubProperty of Subclass

I don't know where you got that idea, but it's not true. Neither is  
subclass a subproperty of equivalentclass.

If you reflect a bit you might see how it actually works. Two  
EquivalentClasss always have exactly the same instances. owl:Nothing  
has no instances. A subclass has a subset of the instances of the  
superclass.

Hence, owl:Nothing is a subclass of everything, since the empty set  
is a subset of every other set. But relatively few named classes  
should be equivalent to owl:Nothing.

> shouldn´t it also return owl:nothing?

As you can see above, no.

> In my tests it returns an empty set.

Which means your class can, sometimes, have some instances. Which is,  
preumably, what you want.

> I think the same holds for equivalent and subProperty, doesn´t it?
> The specs are nice but i don´t think there are the right documents.
> They say what should be returned generally and ideally.

The OWL 1.0 specs do not, in general, define an API should behave. I  
would thing it's perfectly reasonable to have an api function which  
returned all subclasses except owl:Nothing...but the current behavior  
is reasonable too.

Furthermore, as I show above, you are a bit confused on the semantics  
of the constructs which may be blurring your understanding of why the  
API works as it does.

Cheers,
Bijan.