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Re: LANG: compliance levels

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 2 May 2002 11:40:57 +0100
Message-ID: <15569.6073.406864.320305@merlin.oaklands.net>
To: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>
Cc: www-webont-wg@w3.org
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). 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.
>    ----
Received on Thursday, 2 May 2002 06:44:11 GMT

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