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

Graham Klyne wrote:
[...]
> 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.

I'm obviously not being clear.  In

> >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
> >

?X denotes a service that will BUY roses in minimum quantities of 100kg.

There does exist a service that can be bound to ?X.  Its the buyer
service.  That's what we're advertising here.

Or was it ?Y you were suggesting could not be satisfied.


> 
> > > 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.

Then I'm hoping you have now :)


> 
> 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.

Of course it can.  If it can assert that a seller service exists, surely
it can equally well assert that a buyer service exists.  It doesn't know
the difference.

Brian

Received on Monday, 23 July 2001 03:00:19 UTC