Re: Question about representing frame information and unification in PL

On Oct 30, 2008, at 7:45 AM, Srini Ram wrote:

> However, to take another example,
> if you have the following classification
> Person -- has two eyes
>     Blue-eyed person
>     Black-eyed person
>
> Than any object which derives from both blue and black eyed persons  
> should have two eyes (color tbd), not four.
> I guess this is the unification I was wondering about.
>
> I think my question really was, how does Powerloom deal with  
> multiple inheritance
> where the same attribute is defined in two superclasses
> -- in the case of clashing attributes(as in the case above where  it  
> is not clear where the child object should have two blue eyes, or  
> two brown eyes, but because Person has two eyes, we know that the  
> child will have two eyes - we should be able to unambiguously answer  
> questions relating to the number of eyes, but not their color)
> -- in the case of non-clashing attributes(as in the engine example).

The problem is that with multiple skolem values, there isn't any  
principled way to unify them.  So PowerLoom will pretty much just not  
do it.  There will be four skolems, but that doesn't mean there are  
four eyes.  Although in the case where you have a logically  
inconsistent definition.  If you were to try this in, say, OWL 2.0  
where you can have qualified number restrictions, you should get an  
inconsistent ontology.

As I noted before, we haven't put much effort into trying to do a lot  
with cardinality reasoning, so PowerLoom wouldn't really notice that.   
There is also the issue of it not really being that convenient to  
indicate to PowerLoom that two skolems should be distinct, although I  
suppose that something like

    (exists (?s1 ?s2) (and (not (= ?s1 ?s2))  ...))

should work for that.

PowerLoom has only the rudiments of a value cardinality reasoning  
system, and the qualified cardinality relations are just stubs with no  
semantics or reasoning attached.