Re: DAML-S expressiveness challenge #1

>On July 9, Thomas B. Passin writes:
> > [Ian Horrocks" <horrocks@cs.man.ac.uk>
> > To: "David Martin]
> >
> > > What you really want to say is that that the class of
> > > persons who buy diapers is exactly the same as the class of persons
> > > who parented some other person. To do this you should use a
> > > sameClassAs assertion along the lines of (using a pseudo-syntax):
> > >
> >
> > I think it's a good idea to get questions like this set out as clearly and
> > simply as possible before inventing new syntax or vocabulary for them.
>
>Sorry if the pseudo-syntax offended you - I wasn't really intending to
>invent new syntax but just to abbreviate the DAML+OIL RDF syntax, which
>is rather cumbersome for such exchanges as this (someone did promise
>to come up with a "human readable" syntax, but we are still waiting).
>
> >  If
> > you were using predicate logic or KIF, I imagine you'd arrive at something
> > like this:
> >
> > for all persons x it is not true that:
> >     ((x bought diapers) and (x is not a parent))
>
>Using FOL is fine by me, although it has the disadvantage that the
>translation into DAML+OIL isn't always obvious. However, I don't think
>that what you have written does the trick - it certainly isn't
>equivalent to the "pseudo" DAML+OIL I wrote. As I understood it, we were
>trying to express that people buy diapers if and only if they are
>parents. What you have written says that people buy diapers only if
>they are parents. What you needed was to say:
>
>for all persons x it is not true that:
>    (((x bought diapers) and (x is not a parent))
>    or ((x not bought diapers) and (x is a parent)))

You could, but in KIF it would be a lot easier just to say

(forall (?x)(iff (Bought-diapers ?x)(IsParent ?x)))

But the key point is the one Ian brought up earlier in this thread: 
these sentences (in KIF or CGs or DAML+OIL) all say that the two 
predicates (or classes)  have exactly the same instances. If true, 
they are true in *all* interpretations, not just about the particular 
data that has been recorded so far. If sentences like this are 
asserted and then someone finds a non-parent buying a diaper, they 
have generated a logical contradiction.  I don't think that is what 
Martin really wanted to do.

For the record, this issue - of wanting to distinguish between 
logical expressions of meaning, on the one hand, and mere contingent 
facts, on the other - recurs again and again in ontology work, and 
has been the subject of considerable discussion. Nicola Guarino and 
others have argued that a fully expressive ontology language needs 
modal notions such as necessity to distinguish 'rigid' properties 
from mere accidental properties, for example. I mention this only to 
suggest that DAML+OIL isn't likely to be able to keep everyone happy 
over this.

Pat

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Received on Monday, 9 July 2001 20:03:58 UTC