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Re: article on URIs, is this material that can be used by the

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Mon, 11 Jun 2007 17:30:25 +0100
To: Pat Hayes <phayes@ihmc.us> SWEO IG?
Cc: Tim Berners-Lee <timbl@w3.org>, Pat Hayes <phayes@ihmc.us>, Dan Brickley <danbri@danbri.org>, www-tag@w3.org
Message-ID: <f5bejki313y.fsf@hildegard.inf.ed.ac.uk>

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Pat Hayes writes:

>>Stop, you're both right [1].  The (metadata, bits) pair is a
>>representation of the resource.  The resource is a depiction (a kind
>>of representation) of Shakespeare.  To some extent, 'represents' is
>>transitive
>
> Whaaa??? No, it is NOT transitive. A photograph of a book describing a
> statue of George V is not a representation of George V.

I did say 'to some extent'.  A photograph of a painting of George V
surely depicts George V, and an MP3 of a wax cylinder of a player
piano roll of Rubenstein playing the Hammerklavier is still a
rendering of the Hammerklavier.

> The basic problem, seems to me, is that y'all (by which I mean the TAG
> mostly) are using words like "represent" far too loosely. The above
> two sense of represent have very little to do with one another, and
> even less to do with represent as in 'knowledge representation'.

Indeed there are some subtle and complex issues to do with depiction,
rendering, representation and the like, both in their ordinary
language and technical usages.  But surely in many cases (including
all the examples I cited), there _is_ a significant amount of
transitivity, and what's wanted is a careful analysis of what does and
does not 'survive' each step in the chain.  're-presentation' is not
the same as direct delivery -- see lengthy discussions of what it
means to be a map, for instance -- some aspects of the thing
represented are maintained, others are lost -- and therefore in
representations of representations, even more is lost.

I certainly agree that descriptions and representations are
importantly distinct, and that knowledge representation is a bit of a
misleading name (as was acknowledged in the old days by
referring to Semantic Nets and KRL as "description languages", and
latterly by the name "description logic") -- represented knowledge is
not typically itself a representation, but rather a description, of
what it's about.  (Note we don't say e.g. a map is 'about' Edinburgh,
rather it is 'of' Edinburgh, whereas a travelogue is 'about'
Edinburgh, not 'of' it.  I can rephrase your example as follows,
without violence to it:

  A photograph of a book about a statue of George V is not a
  representation of George V.

Using the 'of'/'about' diagnostic, I then convert this to

  represents(photo,book) & describes(book,statue) & represents(statue,G_IV)

- From which I agree, you cannot conclude 

  represents(photo,G_IV)

But working backwards, if we modify the example as follows

 represents(photo,sketch) & represents(sketch,statue) & represents(statue,G_IV)
  
Then I claim we _can_ conclude 

 represents(photo,G_IV)

and that accords with at least _my_ intuition about the corresponding

  A photograph of a sketch of a statue of George V is a representation
  of George V.

ht
- -- 
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                     Half-time member of W3C Team
    2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
            Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                   URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]
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Received on Monday, 11 June 2007 16:30:41 UTC

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