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Re: use/mention and reification

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Mon, 21 Jan 2002 19:17:46 +0000
Message-Id: <>
To: Dan Brickley <danbri@w3.org>
Cc: RDF core WG <w3c-rdfcore-wg@w3.org>
[Dan - my viewpoint shifts through this message ... I'm posting it in case 
it helps expose any more assumptions.]

At 08:42 AM 1/21/02 -0500, Dan Brickley wrote:
>On Mon, 21 Jan 2002, Jan Grant wrote:
> > I still don't understand why you can't pronounce
> >
> >       <sentence> <rdf:Subject> <mary> .
> >
> > as "the sentence has a subject whose referent is (the person) Mary" -
> > ie, if you just change your intuition about what rdf:Subject "means"
> > does this go away?
>Not really. For one, this approach forces the quoting content to share
>worldview with the quoted content about whether the terms used denote. If
>we assume that all URIs denote, and that the term->world mapping is
>static, maybe this isn't a problem. But I'm not sure we've committed to
>those claims yet.

Er, you lost me at the first hurdle.  I don't see a "quoting" context here.

I would expect the term <mary> as object of <rdf:subject> to denote the 
same thing as any other occurrence of <mary> in the same graph.  As far as 
I can tell, all that requires is that interpretation is applied 
consistently across a graph.  Without that, I think the model theory collapses.

>If we define rdf:statement/predicate/subject/object unclearly, we'll make
>some pretty basic mistakes. For example, we might want to define
>'attitude' properties that relate an agent to a statement: 'requests',
>'believes', 'fears' etc. Imagine we had
><Person foaf:name="Jan">
>   <foaf:mbox rdf:resource="mailto:jan.grant@bristol.ac.uk"/>
>   <claims>
>         <rdf:Statement>
>           <rdf:subject rdf:resource="mary"/> <!-- some uri for the cia -->
>           <rdf:predicate rdf:resource="http://example.com/worksFor"/>
>           <rdf:object rdf:resource="cia"/> <!-- some uri for the cia -->
>          </rdf:Statement>
>    </claims>
>If we adopt your re-reading of rdf:subject etc., we lose the ability to
>capture important detail of the content ascribed to Jan.  We would have no
>basis for concluding that you (ie. the person we're ascribing this content to)
>had ever encountered the URI 'some-uri-for-mary'). Since we're solely
>using that URI to point to the individual who is mary.

What you lose, I think, is to ascribe a particular rendering of a statement 
to Jan.  What you gain is the ability to ascribe to Jan some statement that 
had a given interpretation.  (That is, you can make the assertion that Jan 
made a statement that, when interpreted in the context of its utterance, 
had a given interpretation.)

So, I might have been in France last year and heard Jan utter to a passing 
Frenchman "J'ai vu un chat noir" (if you'll pardon my French), and I could 
later say "Jan told the Frenchman that he'd seen a black cat".

I guess it depends on what you regard as the "important detail".  My 
current view is that it's the interpretation, not the exact rendering.

>Imagine we also know that Jan claims '<worksFor> <mary> <kremlin>' and
>'<worksFor> <mary> <MI5>'. It would be easy to slip into thinking that
>this licenses us to believe that Jan is familiar with the fact that the
>uri 'mary' denotes mary, and that he'd understand rdf/xml that used the
>uri 'mary' within rdf:about and rdf:resource as being about this same

Within the same graph, surely it is?

>   That isn't so.  We would however be licensed to believe that
>there was some individual (who possibly-unbeknownst-to-jan happens to be
>named by the URI 'mary') who Jan is claiming worksFor the kremlin, cia and

... but yes, I take your point.

>Hiding (and preserving) URIs within literals protects us from some of this
>slipperyness; our applications will have direct access to the terms used
>in the original content. This is similar to, but less extreme than,
>keeping the original rdf/xml content (complete with charset info, base
>URIs etc) around. There's what they said, and how they said it; the
>reading you suggest is very much 'what they said (but not how they said
>it)'. I think the above example shows that this can put some big limits on
>its uses.

OK, I'm beginning to see what the issue is here.

But I'm still deeply uncomfortable with it.  I need to think about this 
some more.


Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
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Received on Monday, 21 January 2002 14:29:45 UTC

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