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Re: use/mention and reification

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Wed, 23 Jan 2002 11:15:59 +0200
To: ext Graham Klyne <Graham.Klyne@MIMEsweeper.com>, Dan Brickley <danbri@w3.org>
CC: Jan Grant <Jan.Grant@bristol.ac.uk>, Dan Connolly <connolly@w3.org>, RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <B8744BEF.C1A6%patrick.stickler@nokia.com>
On 2002-01-23 0:45, "ext Graham Klyne" <Graham.Klyne@MIMEsweeper.com> wrote:


> So what is the RDF behind Lois' beliefs? (slipping into N3)...
> 
>   [ a foaf:Person ;
>     foaf:name "Lois" ;
>     ex:accepts
>       { [ a foaf:Person ; foaf:name "Superman" ] es:is ex:Strong } ;
>     ex:doesNotAccept
>       { [ a foaf:Person ; foaf:name "Clark Kent" ] es:is ex:Strong }
>   ]
> 
> This way of coding the information has the things whose interpretation is
> possibly local ("Superman", "Clark Kent") expressed as literals, not as URIs.

But how then do we unify the shared beliefs of different individuals
if we use literals rather than URI refs?

E.g.

   [ a foaf:Person ;
     foaf:name "Jimmy" ;
     ex:accepts
       { [ a foaf:Person ; foaf:name "Superman" ] es:is ex:Strong } ;
     ex:doesNotAccept
       { [ a foaf:Person ; foaf:name "Clark Kent" ] es:is ex:Strong }
   ]

How do we know who "Lois" or "Jimmy" really are, and that they are
talking about the same "Superman" or "Clark Kent" if we don't use
URI refs. Isn't that the whole point of URI refs?

I agree with Jan's view that a URI ref denotes an RDF resource, and
whether two or more resources denote the same "thing" in some
universe is a separate issue. It is no different than whether or not
<dc:title> and <foo:title> mean the same thing or whether "5.0"
or "000005" or "5.000000" denote the same value.

Equality of things denoted by RDF resources in a given universe of
interpretation is a separate issue from identity and equality
of RDF resources in an RDF graph.

Reification using URI refs provides consistent identity of RDF
resources without forcing assertion, and quoting URI refs of
resources as literals is just going to add an unnecessary
layer of interpretation.

Much better, I think, to say

--

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns="ex:">

<rdf:Description rdf:about="#Lois">
   <accepts>
      <rdf:Statement>
         <rdf:subject rdf:resource="#Superman"/>
         <rdf:predicate rdf:resource="ex:is"/>
         <rdf:object rdf:resource="#Strong"/>
      </rdf:Statement>
   </accepts>
   <doesNotAccept>
      <rdf:Statement>
         <rdf:subject rdf:resource="#Clark_Kent"/>
         <rdf:predicate rdf:resource="ex:is"/>
         <rdf:object rdf:resource="#Strong"/>
      </rdf:Statement>
   </doesNotAccept>
</rdf:Description>

<rdf:Description rdf:about="#Jimmy">
   <accepts>
      <rdf:Statement>
         <rdf:subject rdf:resource="#Superman"/>
         <rdf:predicate rdf:resource="ex:is"/>
         <rdf:object rdf:resource="#Strong"/>
      </rdf:Statement>
   </accepts>
   <doesNotAccept>
      <rdf:Statement>
         <rdf:subject rdf:resource="#Clark_Kent"/>
         <rdf:predicate rdf:resource="ex:is"/>
         <rdf:object rdf:resource="#Strong"/>
      </rdf:Statement>
   </doesNotAccept>
</rdf:Description>

<rdf:Description rdf:about="#Superman">
   <is rdf:resource="#Strong"/>
</rdf:Description>

</rdf:RDF>

--

Now we have the means to infer that there is some agreement
between the views of Lois and Jimmy, yet none of those views
are actually asserted, insofar as the expression of those
views are concerned -- and we also see that at least some
of their shared views intersect with asserted "real world
knowledge".

The intersections between quoted and asserted knowledge from
the above example shows very nicely in the graph produced
by the W3C RDF validator.

Eh?

Cheers,

Patrick

--
               
Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Wednesday, 23 January 2002 04:15:12 EST

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