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Re: LANG: compliance levels

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 2 May 2002 19:39:58 +0100
Message-ID: <15569.34814.815752.311692@merlin.oaklands.net>
To: Deborah McGuinness <dlm@ksl.stanford.edu>
Cc: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>, www-webont-wg@w3.org
On May 2, Deborah McGuinness writes:
> 
> 
> Ian Horrocks wrote:
> 
> > On May 2, Frank van Harmelen writes:
> > > Jonathan Borden wrote:
> > > >
> > > Ian Horrocks wrote:
> > > > >
> > > > > I would suggest that where universal quantification is being widely
> > > > > used in practice, it is either as a result of its being the only
> > > > > available option and/or the fact that many users assume an implicit
> > > > > existential - it never occurs to them that people all of whose
> > > > > children are doctors may not have any children at all (I would hardly
> > > > > bother telling you what type their children must be if they don't have
> > > > > any children, would I?).
> > >
> > > Ian,
> > >
> > > Arguing that there are different modelling styles is one thing,
> > > arguing that everybody who has a different modelling style doesn't
> > > understand what they are doing is quite another.
> >
> > I didn't say that, and I was not talking about "modelling style"
> > (whatever that is). I was talking about cases of real misuse, or at
> > least of imprecision. Examples are easy to find in the daml ontology
> > library. E.g., in the world fact book ontology all restrictions are
> > universal. I would guess that this is the result of a relatively
> > arbitrary choice when translating from some modelling "formalism"
> > where there is no alternative (or no distinction between universal and
> > existential quantification). In many cases it seems quite clear that
> > existential quantification would be more appropriate. E.g., a property
> > of countries is their totalArea. This is modelled as a universal
> > constraint (if a country has a totalArea then it must be of type
> > xsd;decimal) when it seems more reasonable/precise to use an
> > existential (all countries have a totalArea and it is of type
> > xsd;decimal).
> 
> This is not completely correct.
> What you are really saying as of course you know well with an existential is
> that there is at least one value of totalArea and it is of type decimal.
> You have left open the option for another total area to exist which is not a
> decimal.
> You would have to add that totalArea is functional in order to obtain accurate
> conceptual modeling.

I said it seems MORE reasonable/precise. I was arguing that universal
-v- existential is not always just a matter of style, and that
universal is sometimes used when existential is more appropriate.  I
gave an example from the factbook ontology that I believe supports my
argument.

> One could also argue that stating that at least one of the fillers of totalArea
> is also imprecise conceptual modeling and it is only by the deduction that one
> gets after one states that the role is function, that one gets precise modeling.
> 
> Thus, I do not think you have made your point   or  that the analogous point can
> be made in the opposite direction as I claim I have just made.

This makes no sense to me whatsoever. I believe I made my point very
clearly (that universal is sometimes used when existential is more
appropriate). Of course one may be able to do even better by using
additional constructors such as functionality (I already discussed
this in an earlier email), but that isn't really relevant here. So
what is the analogous point you have made in the opposite direction? I
expect one could find examples where existential is used when
universal would be more appropriate, but I don't see such an example
here.

Ian


> 
> > Note that this doesn't say that we know what the
> > totalArea is or have to specify it, just that a value for the
> > totalArea must exist. In this case I would say that the choice of
> > universal quantification is not a question of style but simply of
> > poor/imprecise modeling.
> >
> > >
> > > Universal restrictions are exactly what is found in many OO languages:
> > > "if slot S has a value, then it is of type X"
> > > I find it hard to believe that entire communities don't understand what
> > > they are writing down.
> >
> > If in these languages universal quantification is the only available
> > option (I suspect that in many cases the precise semantics isn't
> > clearly specified), that would account for why people are using it a
> > lot wouldn't it?
> >
> > Ian
> >
> > >
> > > Frank.
> > >    ----
> 
> --
>  Deborah L. McGuinness
>  Knowledge Systems Laboratory
>  Gates Computer Science Building, 2A Room 241
>  Stanford University, Stanford, CA 94305-9020
>  email: dlm@ksl.stanford.edu
>  URL: http://ksl.stanford.edu/people/dlm
>  (voice) 650 723 9770    (stanford fax) 650 725 5850   (computer fax)  801 705
> 0941
> 
Received on Thursday, 2 May 2002 14:43:15 GMT

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