W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > July 2001

Re: A use case for anon nodes - action from telecon

From: Graham Klyne <Graham.Klyne@Baltimore.com>
Date: Fri, 20 Jul 2001 12:38:29 +0100
Message-Id: <5.1.0.14.2.20010720121601.039033e0@joy.songbird.com>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: rdf core <w3c-rdfcore-wg@w3.org>
At 10:36 AM 7/20/01 +0100, Brian McBride wrote:
> > > > There seems to me to be no way of rendering this statement using just
> > > > existential quantification.
> > >
> > >As  you see, I've made an attempt.
> >
> > Good, thanks!
> >
> > The problem I now see is that this asserts the existence of the required
> > service:
> >
> >    thereExists ?X which is the object of (advert123 description ?X)
> >    (etc)
>
>I think the intent here was to assert the existence of the buyer service,
>which does exist (for some definition of exist).
>
>The game that is being played here is that this example is not being
>presented as a query.  Rather than say please find me X, one is saying
>exists Y such that Y is a consumer of X.

I'm fine with asserting the existence of the buyer service.  The problem I 
have is that the *description* of the buyer service asserts the existence 
of something that may not actually exist.

> > But the apparent intent of this is ask if such a service exists.  Do I
> > detect a "gensym" error?
>
>What's a gensym error?

An expression Pat used recently, if I get it right, to describe logical 
errors introduced by human interpretation of a symbol in an expression 
without any logical basis for that interpretation.

In this case, we know what a "buyer" is, and what a "seller" is.

The two examples you gave in 
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jul/0240.html are 
identical modulo a name change and a quantity.  (Pedagogically, they could 
equally have been stated using the same quantity so that the only 
difference was a name change.)

Yet we infer that in one case the goods offered for sale definitely exist, 
but in the other case no assertion is made about their existence.  There 
seems to be no *logical* basis for this difference in interpretation when 
the only difference is a naming difference.

Currently, it seems to me that the Existential-Conjunctive (EC) subset of 
first order logic, hence RDF as I understand it, is incapable of expressing 
the buyer proposition without actually asserting the existence of that 
which is to be purchased.

> > > >
> > > > This may be a compelling use-case, but I don't see any sanction for 
> this
> > > > usage in M&S 1.0, and as such would suggest it be deferred to V2.0.
>
>Then you must show how it is different from the Lassila example in M&S.

See above.

> > >
> > >What is the difference between this and the example in:
> > >
> > > 
> http://lists.w3.org/Archives/Public/www-archive/2001Jun/att-0021/00-part#41
> >
> > That case asserts the existence of the un-identified individual.
>
>This case asserts the existence of an un-identified service.

And more.  See above.

#g


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Graham Klyne                    Baltimore Technologies
Strategic Research              Content Security Group
<Graham.Klyne@Baltimore.com>    <http://www.mimesweeper.com>
                                 <http://www.baltimore.com>
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Received on Friday, 20 July 2001 08:01:25 EDT

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