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Re: why I don't like named graph IRIs in the DATASET proposal

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 4 Oct 2011 16:08:39 +0100
Cc: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>
Message-Id: <BD11C338-1BE4-4858-92CF-DE2398A0CEB2@cyganiak.de>
To: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
On 2 Oct 2011, at 18:06, Pierre-Antoine Champin wrote:
> As you stress it, RDF does not dictate which IRI should denote which
> resource (including graphs). I don't think I ever suggested to change that.
> 
> However, RDF dictates that each time I use the same IRI (as a node), it
> denotes the same resource.

No, it doesn't.

RDF Semantics is concerned with the interpretation of *individual RDF graphs*.

As far as RDF Semantics is concerned, the same IRI may identify completely different things in different RDF graphs.

It is the social contracts and conventions of the web that encourage us to converge on a single unique referent for each IRI. This is orthogonal 

For example, in this triple:

   <#me> foaf:homepage <http://richard.cyganiak.de/>.

we all know what the subject of the encoded statement is. But that's not because of RDF Semantics. As far as RDF Semantics is concerned, <http://richard.cyganiak.de/> denotes a completely arbitrary resource. It's conventions that allow us  and the software we create  to understand that the target is a web page that can be accessed via a browser and so on.

This mechanism *works*.

I suggest to treat graph names in exactly the same way. When we assert inside some RDF dataset:

   <#me> ex:assertsGraph <#graph1>.

then as far as RDF Semantics is concerned, <#graph1> denotes an arbitrary resource. It's conventions  and the definition of ex:assertsGraph  that allow us, and our software, to understand that this talks about a different graph within the same dataset.

When you and Pat demand that the denotation of graph names in RDF datasets be fixed to the graph, then you conveniently ignore the fact that RDF Semantics currently doesn't have the power to fix the denotation of *anything* (except the RDF(S) built-ins), and *always* defers to convention for establishing the connection between IRIs and things. RDF works nevertheless. Why should it be any different for graphs?

Best,
Richard
Received on Tuesday, 4 October 2011 15:09:20 GMT

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