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Re: Semantics of rdf:Statement

From: Richard Cyganiak <richard@cyganiak.de>
Date: Fri, 20 Jul 2007 20:26:08 +0200
Message-Id: <103ABBB8-BCB9-4A65-94D9-29984AA22698@cyganiak.de>
Cc: semantic-web@w3.org, Alexander Boer <aboer@uva.nl>, Thomas Gordon <thomas.gordon@fokus.fraunhofer.de>
To: Rinke Hoekstra <hoekstra@uva.nl>

Rinke,

On 20 Jul 2007, at 12:36, Rinke Hoekstra wrote:
> I have a question regarding the rdf:Statement mechanism for  
> reification: what is the semantics of an rdf:Statement consisting  
> of multiple subject, predicate and object properties?

The RDF spec doesn't define any semantics at all for reification.  
Thus, in standard RDF, the example you've given below is just a bunch  
of meaningless triples.

People who use RDF reification assign their own private, local  
meaning to the reification vocabulary. That's fine as long as you are  
in a closed system. Of course you have to be very careful when  
exchanging reified statements with other parties. (In other words:  
You probably shouldn't.)

Regarding your example with multiple rdf:subject, rdf:predicate and  
rdf:object statements, all I can say is: Don't.

Best,
Richard


>
> As far as we can tell, the RDF spec. is silent on this issue, and  
> leaves implicit whether there is a 1:1 mapping between a triple and  
> its reification as a rdf:Statement.
>
> Supposing this 1:1 mapping holds, the following RDF should be  
> incorrect, or at least problematic:
>
> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
>     <rdf:Statement rdf:ID="S1">
>       <rdf:subject rdf:resource="http://www.leibnizcenter.org/ 
> information/people/rinke-hoekstra" />
>       <rdf:subject rdf:resource="http://www.leibnizcenter.org/ 
> information/people/alexander-boer" />
>       <rdf:predicate rdf:resource="http://description.org/schema/ 
> Creator"/>
>       <rdf:predicate rdf:resource="http://description.org/schema/ 
> Fish"/>
>       <rdf:object rdf:datatype=
>          "http://www.w3.org/2001/XMLSchema#string">Rinke Hoekstra
>       </rdf:object>
>       <rdf:object rdf:datatype=
>          "http://www.w3.org/2001/XMLSchema#string">Alexander Boer
>       </rdf:object>
>     </rdf:Statement>
> </rdf:RDF>
>
> The above example implicitly states that http:// 
> www.leibnizcenter.org/information/people/rinke-hoekstra and http:// 
> www.leibnizcenter.org/information/people/alexander-boer, and http:// 
> description.org/schema/Creator and http://description.org/schema/ 
> Fish pairwise point to the same resource. This is fine.
>
> However, for datatype resources this is really problematic as the  
> above RDF states that the *strings* "Rinke Hoekstra" and "Alexander  
> Boer" are equal. Something which is clearly not true...
>
> The W3C RDF Validator validates the above RDF as being correct. Is  
> this intended?
>
> Thanks,
>
> 	Rinke Hoekstra
>
> -- 
> ----------------------------------------------
> Drs. Rinke Hoekstra
>
> Email: hoekstra@uva.nl   Skype:  rinkehoekstra
> Phone: +31-20-5253499    Fax:   +31-20-5253495
> Web:   http://www.leibnizcenter.nl/users/rinke
>
> Leibniz Center for Law,         Faculty of Law
> University of Amsterdam,           PO Box 1030
> 1000 BA  Amsterdam,            The Netherlands
> ----------------------------------------------<hoekstra.vcf>
Received on Friday, 20 July 2007 18:26:44 UTC

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