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Re: Reification: proposed resolution

From: Frank Manola <fmanola@mitre.org>
Date: Tue, 12 Feb 2002 18:12:28 -0500
Message-ID: <3C69A15C.2080307@mitre.org>
To: Brian McBride <bwm@hplb.hpl.hp.com>
CC: RDF Core <w3c-rdfcore-wg@w3.org>
Brian McBride wrote:

> Following up on Frank's excellent reification process, and the decision 
> we made last week support the provenance use case, I'm wondering if we 
> can move forward on reification.  I wonder if at this weeks telecon we 
> can decide that the answer to the question:
> Does
>   <stmt1> <rdf:type> <rdf:Statement> .
>   <stmt1> <rdf:subject> <subject> .
>   <stmt1> <rdf:predicate> <predicate> .
>   <stmt1> <rdf:object> <object> .
>   <stmt2> <rdf:type> <rdf:Statement> .
>   <stmt2> <rdf:subject> <subject> .
>   <stmt2> <rdf:predicate> <predicate> .
>   <stmt2> <rdf:object> <object> .
>   <stmt1> <property> <foo> .
>   entail:
>   <stmt2> <property> <foo> .
> is NO.

I hope so too.

> Regarding Graham's entailment:
> <ex:subj> <ex:prop> <ex:obj> .
> entails
>      _:r <rdf:type> <rdf:Statement> .
>      _:r <rdf:subject> <ex:subj> .
>      _:r <rdf:predicate> <ex:prop> .
>      _:r <rdf:object> <ex:obj> .
> Whilst I see the sense behind it, I'm a bit concerned by the practical 
> implications of all the statements in my graph entailing their 
> reifications.  So from a standpoint of simplicity and pragmatics, I 
> propose that there are NO other entailments in the model theory to do 
> with reification.


What do you see the practical implementations of this entailment being? 
  Given the view of

<ex:subj> <ex:prop> <ex:obj>

as a "stating" (inscription, statement occurrence, aka "triple"), I 
don't see how we can logically (?) deny that the presense of this triple 
entails that "there exists a statement with [such and such 
characteristics]".  Haven't we just said it?  Does the problem have to 
do with what we say instances of <rdf:Statement> are (statements or 
triples)?  I.e., we can't say "there exists a statement..." because it 
isn't one, it's a triple?

A more practical issue, it seems to me, is that even if all the 
statements in your graph entail their reifications, what's the point? 
There's no way (in RDF) to associate any generated reifications with the 
original triples.  Conversely, if I have some way of identifying triples 
by associating URIs with them, I can define triples expressing 
provenance or anything else about them without any special reification 
syntax.  Mind you, given that I can identify individual triples in this 
way, I still might find it useful to have a "standard" vocabulary, like 
<rdf:predicate>, for referring to the various parts of the triples, but 
that wouldn't necessarily have anything to do with provenance.


Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Tuesday, 12 February 2002 18:07:35 UTC

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