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Re: Uniform access to descriptions

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 12 Apr 2008 00:00:54 -0500
Message-Id: <p06230900c425ef0995bc@[]>
To: wangxiao@musc.edu
Cc: noah_mendelsohn@us.ibm.com, Jonathan Rees <jar@creativecommons.org>, Phil Archer <parcher@icra.org>, "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, "www-tag@w3.org WG" <www-tag@w3.org>
At 12:57 AM +0100 4/12/08, Xiaoshu Wang wrote:
>Pat Hayes wrote:
>>>Question 1: Is there a difference between Representation and Resource?
>>Um... it depends what you mean. They are different/ concepts/ 
>>(categories, classes, properties), to be sure, since there are may 
>>resources that aren't representations (and IMO - though others may 
>>differ - there are also representations which aren't resources). 
>>But they need not be exclusive: something can be both a 
>>representation and a resource. In fact, it is exactly these cases 
>>which seem to give us the most trouble in this exchange. For 
>>example, a home page is a resource but it might also be reasonably 
>>called a representation of the person it describes. (I'm assuming 
>>here that 'representation' is being used in a broad sense, not as 
>The definition of /representation/ is very precise and clear.  It is 
>whatever the stuff (within the web, it is a byte-stream) that 
>eventually reaches to the client.  I think you perhaps have though 
>it as something-else?

OK, what you are here calling 'representation' is what I have been 
calling 'awww:representation' or sometimes tag:representation. This 
is a *very* special sense of the English word 'representation', even 
when that word is understood in a technical sense. Since SWeb 
languages such as RDF and OWL  are in a family of formalisms which 
everywhere except inside the Web community are called 'knowledge 
representation languages', this special usage is unfortunate. In my 
answer, I was using the word in the more general sense, as noted. I 
had formed the impression from your earlier messages that you also 
were using it in a wider sense.

>Is this the case, because otherwise I cannot follow your answer.

Im not surprised, given the above-noted disconnect. OK, let me answer 
again, this time assuming that you mean 'representation' to refer to 

Yes, there is a difference. The two categories are disjoint. (Other 
answers given in-line below, with this revised understanding of your 

>>>(1a): Yes.  Representation -> Resource; (here let's name "->" as identify).

No, the awww:representation does not identify the resource. The URI 
identifies the resource.

>>>Question 2: Can one resource has multiple Representation?

Yes. There can be dynamic resources which change with time, so that 
they emit different awww:representations at every GET. (Eg an on-line 
digital clock.) These obviously can have multiple 
awww:representations. Also, content negotiation can  give alternative 
awww:representations of a single resource.

>>>Question 3: What does a URI denote?
>>A thing. Or, if you prefer the older terminology, a resource.

This answer still holds.

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Received on Saturday, 12 April 2008 05:01:35 UTC

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