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

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 11 Jun 2007 12:37:41 -0500
Message-Id: <p06230909c2932f19fae7@[]>
To: ht@inf.ed.ac.uk (Henry S. Thompson)
Cc: Tim Berners-Lee <timbl@w3.org>, Pat Hayes <phayes@ihmc.us>, Dan Brickley <danbri@danbri.org>, www-tag@w3.org

>Hash: SHA1
>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
>>  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.

Rendering, yes. Good word. That is, if you listen to the final thing, 
you will, more or less, hear the Hammerklavier. But this amounts to 
something like 'suitably formatted copy of'; it is hardly a general 
notion of representation (though it does seem to be what the TAG 
writings mean by this word, insofar as I can understand them.) It 
might be better to call this relationship 'rendering' rather than 
'representation'. An audiobook read by the author is a representation 
(in different senses) of both the book and the author; read by 
someone else it is still a representation of the book.

>>  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

I find them all rather implausible when one uses the word 
'representation'. I once heard an old recording of Maria Callas on my 
car radio and mused on how many different forms and technologies it 
had been put through from being the actual sound of her voice 
entering a microphone to the sound coming out of my speakers. It was 
plausibly about a dozen and could have been more. But this is not 
what we usually mean by 'representation' (is it? Not what people I 
talk to mean, anyway.) We don't say, when transcribing vinyl to MP3, 
that we are *representing* the music (still less the musicians 
playing it). We say we are re-recording it. Now, re-recording audio 
is what one might call transitive-with-noise; similarly, visual 
rendering of a visual image (photo of a sketch of a painting...) is 
also. But many forms of representation are completely different from 
these re-formatting or re-recording operations. It can hardly be held 
to be the normal or typical case for representations in general. If 
one inserts a transcription into musical notation into the vinyl-MP3 
chain, for example, transitivity breaks immediately; yet surely this 
is still a representation of the music.

>, 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

I'd say rather than descriptions are one kind of representation, and 
indeed a very important one. Renderings are another kind, and are 
fundamentally different from descriptions. Description-of is not 
transitive. Rendering-of might be, with care.

>, 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.

You are using "representation" here in a very idiosyncratic way.

>   (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.

What do we say for an ontology of Edinburgh? Is it /of/ or /about/ 
Auld Reekie? BTW, I note that a picture /of/ Edinburgh might be 
/about/ something else entirely, such as castles or whisky.

>  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) & 
>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.

Fair enough for that example. But as I say, you seem to be using 
"represent" in a very particular and by no means universally 
understood way. Which is fine, I guess, as long as you make sure to 
make this usage vividly clear to everyone else. And be ready for the 
long tail of misunderstanding that will ensue :-)


>- --
>  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/
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Received on Monday, 11 June 2007 17:37:50 UTC

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