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

From: Pierre-Antoine CHAMPIN <pachampi@caramail.com>
Date: Wed, 18 Oct 2000 10:21:25 -0400
To: Tom Van Eetvelde <tom.van_eetvelde@alcatel.be>, www-rdf-interest@w3.org
Message-ID: <971882484001391@caramail.com>
Quite interesting, indeed.
But I see two problems with your proposition :

The first one may seem a detail, but has not yet been 
settled once for all :
RDF does not allow anonymous nodes.
(so called anonymous resources are a syntactical artifact, 
but have no correspondance in the model).

We have to decide once for all whether such nodes exist in 
the RDF model, and if so, what they mean.
(Your proposition is an interesting first step in that way).


The second problem I see is the following:

 [*]
 ^
 |
 (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) <= (beverage x)

"John drinks everything, and everything is a beverage"
 forall x, (drink John x) ^ (beverage x)

RDF was initially proposed to express simple facts.
Rules look as "meta-facts" to me, so we need a meta-
language to express rules about RDF facts.
The good thing with RDF is that it can always(?) be used as 
a meta-language, including for itself (see RDFSchema).

So I would rather express that "John drinks any beverage" 
using "two-level" RDF :

 [Graph1]--(implies)-->[Graph2]

Graph1:

 [var:1]--(type)-->Beverage

Graph2:

 [John]--(drinks)-->[var:1]

Might look cumbersome, but look sound to me.
Have a look at Graham Klyne's paper about Contexts in RDF,
it might help in getting convinced :)

http://public.research.mimesweeper.com/RDF/RDFContexts.html

 Pierre-Antoine

PS: wouldn't that thread be more appropriate on www-rdf-
logic ??
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Received on Wednesday, 18 October 2000 10:22:00 GMT

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