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Re: Semantics of rdf:Statement

From: Rinke Hoekstra <hoekstra@uva.nl>
Date: Mon, 23 Jul 2007 10:59:20 +0200
Message-ID: <46A46DE8.9020109@uva.nl>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
CC: semantic-web@w3.org, Alexander Boer <aboer@uva.nl>, Thomas Gordon <thomas.gordon@fokus.fraunhofer.de>
Hi Bijan,

Bijan Parsia wrote:
*snip*
> This isn't an insane reading but I don't immediately see that from the 
> RDF semantics. Consdier:
> 
> """Semantic extensions MAY limit the interpretation of these so that a 
> triple of the form
> 
> aaa rdf:type rdf:Statement .
> 
> is true in I just when I(aaa) is a token of an RDF triple in some RDF 
> document, and the three properties, when applied to such a denoted 
> triple, have the same values as the respective components of that 
> triple."""
> 
> Ok, first this is a semantic extension and a MAY, so I'm not sure how 
> much weight you want to give it over your reading. Second notice that a 
> reification does *not* (necessarily) say anything about the graph in 
> which the reification appears....it just says there is *SOME* graph that 
> contains the corresponding triple (and I'm  not sure exactly how to 
> interpret the existential there..some concrete graph? A model with a 
> graph in it? Is every reification always true if we are platonists 
> (since all graphs *exist*, including the graph with the single triple 
> corresponding to the reification).
> 
> So, this would suggest that the multiple subjects might just mean that 
> SOME GRAPH thinks that they are the same. (But this would not be 
> expressible in RDF. You might expect a reification aware system to 
> entail the requisite sameas.)

That indeed is a significantly weaker semantics than my interpretation, 
and I understand from Richard's reply that an implementation of this in 
a reification aware system would be non-standard.

> But another reading could be that rdf:subject is both functional *and* 
> lexigraphicly sensitive. That is, your example would be *inconsistent* 
> since there is no *syntactic item* that is a triple with two subjects. I 
> think this is the more likely reading since the statement denotes *one* 
> triple (per graph). And in point of fact, triple identity (not logical 
> equivalence) is determined by the particular items in each slot.
> 

Ok, that sounds a lot better.

*snip*
> Well that would just be inconsistent on your reading...why not? That's 
> because of the built in equality theory, but you can imagine that you 
> had an owl:differentFrom which made your subjects inconsistent too. You 
> are proposing that the reification vocabulary is functional...so if it 
> you have multiple objects which are differentFrom each other you SHOULD 
> get an inconsistency.

Ok

> 
>> The W3C RDF Validator validates the above RDF as being correct. Is 
>> this intended?
> 
> The RDF validator does no reasoning of any kind, afaik, so it's not 
> surprising that it doesn't do an optional + non-standard extended 
> reasoning :)
> 
> That is, your form is a *syntactically* correct graph, and the standard 
> semantics are so weak as to always be consistent, and my reading of the 
> only suggested extension in RDF semantics suggests both the 
> multisubjects and multiobjects make the reification inconsistent. But 
> there's clearly another reading wherein the subjects can be consistent 
> and the objects not.
> 
> Hope this helps.

Indeed it does, many thanks.

-Rinke
> 
> Cheers,
> Bijan.

-- 
----------------------------------------------
Drs. Rinke Hoekstra

Email: hoekstra@uva.nl   Skype:  rinkehoekstra
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Received on Monday, 23 July 2007 08:59:26 UTC

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