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

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 23 Jul 2001 21:34:57 -0700
Message-Id: <v0421011eb782a78da1a7@[130.107.66.237]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
>Graham Klyne wrote:
> >
> > At 11:27 AM 7/19/01 +0100, Brian McBride wrote:
> > >Loosely in English it means advert123 is for a service that will
> > >buy roses in quantities of at least 100.
> > >
> > >                      advert123 role buyer
> > >and  thereExists ?X  advert123 description ?X
> > >                      ?X        product      roses
> > >      thereExists ?Y  ?X        minQuantitiy ?Y
> > >                      ?Y        units        kg
> > >                      ?Y        minValue     100
> > >
> > >
> > > >
> > > > 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).

Look at the assertions in your example, above. There are two 
existential claims made in there. One says that something (X) exists 
which bears the description-1 (ie the inverse of description) 
relation to advert123 and the product relation to roses and the 
minQuantity relation to some other thing Y.  X could be a 'service', 
sure. But what kind of thing is Y? It bears a units relation to kg 
and a minValue relation to 100. It sounds like a sale, or a 
transaction, or maybe a quantity of roses. But whatever it is, the 
sentences only assert that *one* of it exists. There is nothing here 
that could possibly convey what is meant by the English gloss of "a 
service that sells roses in quantities of at least 100 kg" (that is a 
hell of a lot of roses, by the way) , since that gloss uses the 
plural ("quantities"), but there isn't anything in the logical 
version that implies more than one of anything.

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

Assuming that a formal structure means more than it really does just 
because it seems to mean that when you read it as if it were English. 
Comes from a famous AI paper by Drew McDermott where he suggested 
that all 'intuitive' names be replaced by gensyms (LISP for genids) 
before you try to figure out what the axioms mean.

>
> >
> > > >
> > > > 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.

The difference is that the Lassila example is purely existential, but 
this isn't.

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

Fine; but what it says about it is that it is connected with the 
existence of an un-identified quantity of roses. Not any such 
quantity: just one. You had better move fast if you want to buy a 
rose.

Pat

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Received on Tuesday, 24 July 2001 00:34:51 EDT

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