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Re: Variables in rdf (Re: capturing 'foreall' in a graph picture)

From: Pierre-Antoine CHAMPIN <pachampi@caramail.com>
Date: Thu, 19 Oct 2000 07:22:27 -0400
To: www-rdf-interest@w3.org, Tom Van Eetvelde <tom.van_eetvelde@alcatel.be>
Message-ID: <971958175031045@caramail.com>
> -------Message d'origine-------
> De : Tom Van Eetvelde <tom.van_eetvelde@alcatel.be>
> Date : 19/10/2000 12:20:04

[About anonymous nodes]
Note that I prefer talking about anonymous nodes rather 
than anonymous resources, since the latter is (mis?)used in 
the RDF spec.

> I see anonymous resources as the modelling of the 
concept 'some specific unnamed thing'.

agreed

> That's what the parser needs to do: when a
> graphically empty node is encountered, give it an ID like 
genid0. Keep this name for local RDF
> processing and drop it again when the processing ends. 
Your resource goes back to anonymity. When
> enough people want to say something about it, eventually 
it will get a name (ID).

Except that the RDF 1.0 XML syntax does not allow any kind 
of graph involving anonymous Descriptions (namely, if more 
than 1 arc points to it).

[About modelling FORALL]
I'm sorry about my example, my mail client appeared to trim 
some spaces. The (type) arc was meant to come from the 
anonymous node, in the center.
It should be corrected below.

> > [*]
> > ^
> > |
> > (type)
> > |
> > [John]--(drinks)-->[ ]--(type)-->[Beverage]
> >
> > Would the graph above mean :
> >
> > "John drinks every beverage"
> > forall x, (drink John x) => (beverage x)
> >
> > "John drinks only beverages"
> > forall x, (drink John x) 
> >
> > "John drinks everything, and everything is a beverage"
> > forall x, (drink John x) ^ (beverage x)
> >
> 
> With my modelling rules, none of the above. I follow root 
to end.

Ahem... root to the end works fine with a path, but a 
graph...
Anyway, you simply AND the statements, so you read it as 
the 3rd proposition. Am I wrong ?
("John drinks X, X is everything, X is a beverage"
 <=> "John drinks everything and everything is a beverage")

> But based on hard facts, John cannot be everything and so 
the graph contains an error.

interesting question :
what would mean a non-anonymous resource with type [*] ??


> My original viewpoint was that RDF has implicitly the 
quantifier 'exists'. So why not
> adding 'foreall'? You clearly see a 'foreall' as a 
quantifier of a different level than quantifier
> 'exists'.

Not exactly. But since RDF lacks negation, disjunction and 
(hence) implication, FORALL can only be used to express 
universal properties (like "everything is a beverage"), 
which is not very useful...
Looks more like we can only express terms, and that we lack 
expression power to express formulae.

 Pierre-Antoine

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Received on Thursday, 19 October 2000 07:22:27 GMT

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