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Re: No model theory for reification?

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Thu, 10 Jan 2002 23:07:12 +0000
Message-Id: <5.1.0.14.2.20020110224717.03867a60@joy.songbird.com>
To: Dan Brickley <danbri@w3.org>
Cc: <w3c-rdfcore-wg@w3.org>
At 11:40 AM 1/10/02 -0500, Dan Brickley wrote:
>How so? Giving a clear definition for rdf:Statement, rdf:predicate,
>rdf:object and rdf:subject might avoid the stating/statement problem. If
>we fail to define rdf:Statement clearly, we'll continue to have
>stating/statement problems. I can't see how merely saying " rdf:statement
>and p/s/o are 'reserved for quoting, provenance etc." fixes this problem.
>
>One way to be clear when defining classes is to give identity conditions
>for members of the class, eg. specify whether members of rdf:Statement
>are uniquely picked out by their predicate/subject/object properties. I
>suspect that if we explore that route, we'll find the statement/stating
>confusion unwravels into the need to be more careful distinguishing URIs
>from the resources they name.

I'm sympathetic with what you say here, but I'm not sure that there's much 
we *can* (easily) say about a statement within the RDF framework as 
currently formalized.

We might say that the intended interpretation of any instance of 
rdf:Statement is that it denotes some RDF statement.  But what does that 
actually mean?  What properties does an rdf:Statement instance have that 
distinguish it from any other RDF resource?

You suggest identity conditions.  But I think that could take us into an 
area of conflict with other work (DAML+OIL/WOL) that build on 
RDF.  Architecturally, I think that core RDF is the wrong place to make 
this kind of assertion.

One thing that I can imagine doing, but something that I think is beyond 
our current charter, is to have a way of relating an rdf:Statement instance 
to a truth value;  i.e. a way of saying that an rdf:Statement corresponds 
to an asserted triple.  A simple example might be similar to the style of 
RDFS-entailment, such that:

     s a rdf:Statement ;
       rdf:predicate pred ;
       rdf:subject   sub ;
       rdf:object    obj ;
       rdf:hasValue  rdf:True .

statement-entails:

       sub pred obj .

(I don't think this particular approach is especially useful;  e.g. for 
provenance we'd want to be able to make the entailment also depend in some 
way on expressed trust in the source of the statement, but I think that's 
still an area for experimentation.)

Earmarking the vocabulary and indicating it's intended interpretation 
without saying anything else (yet) about its semantics, as Jeremy suggests, 
possibly leaves open the path to some future enhancements, without 
committing to exactly what they would be until we have some experimental 
experience.

#g


------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
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Received on Thursday, 10 January 2002 18:33:20 EST

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