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

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 6 Oct 2011 11:06:07 -0500
Cc: <richard@cyganiak.de>, <pierre-antoine.champin@liris.cnrs.fr>, <public-rdf-wg@w3.org>
Message-Id: <443F1B6E-9E2F-4824-B5EE-778BAD066021@ihmc.us>
To: Peter Frederick Patel-Schneider <pfps@research.bell-labs.com>

On Oct 6, 2011, at 5:54 AM, Peter Frederick Patel-Schneider wrote:

> From: Pat Hayes <phayes@ihmc.us>
> Subject: Re: why I don't like named graph IRIs in the DATASET proposal
> Date: Wed, 5 Oct 2011 18:05:04 -0500
>> On Oct 4, 2011, at 10:08 AM, Richard Cyganiak wrote:
>>> 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.
>> Yes, it does. 
> Are you sure, Pat, especially formally?
> peter

Well, formally, it requires that any RDF graph has an interpretation. Now, suppose a URI U occurs in a graph G where it is (for reasons that need not detain us here) required to denote some thing, and also occurs in some other graph H where it is similarly required to denote some other thing, different from the first thing. Now consider the graph (G union H). If both requirements are in force, this graph cannot be given an RDF interpretation. Which violates the RDF semantics spec. So by modus tollens, those two requirements, taken together, violate the spec. 

So perhaps the wording should be, that RDF dictates that whenever you use an IRI, it *could* denote the same resource.

Note, this is not merely that (G union H) is inconsistent (= false in all interpretations) but rather that it is *uninterpretable*, ie has no semantic interpretations *at all*. 



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Received on Thursday, 6 October 2011 16:06:48 UTC

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