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Re: The meaning of "representation"

From: Tim Berners-Lee <timbl@w3.org>
Date: Sat, 24 Nov 2007 19:09:31 -0500
Cc: www-tag@w3.org, Mikael Nilsson <mikael@nilsson.name>, Chimezie Ogbuji <chimezie@gmail.com>
Message-Id: <2D5E141D-6679-489B-857A-4C1907ED3562@w3.org>
To: wangxiao@musc.edu


You have obviously put a of of thought into the system you are  
building, and the
document, <http://dfdf.inesc-id.pt/tr/web-arch>, you have created  
about the the architecture.

You quote Max Plank, "As Max Planck has puts it, "a new scientific  
truth does not triumph by convincing its opponents and making them see  
the light, but rather because its opponents eventually die, and a new  
generation grows up that is familiar with it [14]."

I feel that your document presents an alternative architecture, but an  
architecture is not a scientific truth.
it is a conscious design of a system.  To the extent hat your document  
presents an alternative architecture, l could let it be as Plank  
suggests. However:-

1) we a designing a system, not finding scientific truths. We are  
designing a system for communal use, and so common understanding is  
important for deployment and interoperability.  This is not  the case  
with scientific truths:  the fact that people don't understand them  
doesn't make them less so.

2) You document is unfortunately in places based on what I consider a  
misunderstanding of the AWWW. To the extent that it misrepresents the  
terms used in the AWWW, I feel a correction is in order.

I think that the core of this may be two sources of confusion.

a) The definition in AWW resources "all of their essential  
characteristics can be conveyed in a message" does not speak to where  
you are coming from. You take "essential characteristics" as meaning  
"Properties' rather than " content".  So, not having understood that,  
you are happy to consider Pat to be one.  That I think is a problem  
with that definition.  However, remember natural language is an  
imprecise  tool for making these definitions, and efforts is needed on  
the part of reader as well as writer. An Information Resource is  
information.  Pat is not.

b)  Roy Fielding's thesis, while it helps in many resects, does not  
differentiate between resources and information resources.   This was  
pre-semantic web, and so the question of whether a URI identified a  
person or a person's web page was not putto the test.  Roy uses the  
term "resource" throughout, and has as you say questioned the use of  
the term 'Information resource".   I have felt that distinguishing  
between a person and their web page is for the semantic web very  
important.  I also feel that it was important to allow HTTP URUs for  
web pages to be used to identify web pages, as many things like Dublin  
Core, Creative Commons, and so on, had already started using the URI  
of the document for many things such as authorship, licensing, etc  
which really are forcible about  the document rather than its subject.

You have, Xiaoshu, a very different view of the world, and you use  
terms differently, so experience tells me it will be hard to explain  
to you.

You maintain that for various reasons  the concept of an information  
resource is not useful, and only a detailed annotation of the document  
is the only things which will tease these apart.

Many places I agree. Like using the word "denotes" rather than  
"identifies" is fine.

A few random places where we differ:

- You try to make an architecture in which Pat Hay's famous page is  
true. IMO his page is false, and misleading.  When Pat tries to  
generate random content to illustrate points of argument, that doe  
snot mean one should all try to cater to them.

- You say a Representation is different from the "content of the  
representation". However, as the representation is a set of bits, its  
identity is is contents, IMO.

-  If I understand correctly, I think you use content-negotiation for  
distinguishing between the binary data DFDF things and the RDF  
metadata DFDF things, which are completely different.  One is not   
substitute  for the other.  Content negotiation is inappropriate.    
This may be a source of great confusion.

- You at one point propose, to counter the need for IR as a first- 
class object,  double sets of vocabulary, one set for talking about  
the document and one its subject.  This has been suggested in the past  
mid-argument, I forget where exactly.   I find that approach  
unsatisfactory for a number of reasons.

   - You can't use arbitrary predicates, without having some mechanism  
for generating them.
   - I can talk about the author, licensing and expiry data of a  
document, but also about about the other document which this document  
is about.
   - Sometimes there really is no obvious subject of a document at all.

You also say a lot of things which make sense, and apply to the actual  
architecture of the web as I understand it -- so it is possible that  
some permutation of terms will to a certain extent map your  
architecture and mine better.  Your  piece about who to believe about  
cats and dogs I agree with in general, and i think the AWWW is  
consistent with that the conclusions about Cats and dogs, though not  
about your use of terms in explaining it.

You say there is much confusion. there is a laos a lot of code which  
works.  The linked data projects,  for example, uses content  
negotiation, and URIs with hash or slash in different cases, and the  
code I write fro it uses the concept of Information Resource as a core  
concept to great benefit.

I will see whether I have time to transcribe my margin notes on your  
document,  I am not sure when.   Perhaps I should write something  
explaining what an Information Resource is better. I have tried  
before.   I am not sure when I will get around to it.


On 2007-11 -13, at 05:09, Xiaoshu Wang wrote:

> I have finished the writing about the subject. The URI is http://dfdf.inesc-id.pt/tr/web-arch 
> .
> In short, I think the current AWWW document should be modified to  
> emphasize the following two points:
> (1) The abstract nature of "resource" with regard to the web.
> (2) The role of URI as an interface, in addition to a name, for the  
> web
> I think the failure to recognize the above two points are the  
> reasons for the faulty impression of URI's ambiguity and debate  
> about "information resource".  As for the latter, I think  
> httpRange-14 answered a wrong question because 200 should indicate  
> an informational *URI* but not an information *resource*.
> Xiaoshu
> Xiaoshu Wang wrote:
>> Mikael Nilsson wrote:
>>> Now, we're seeing a spectrum of views on what a "representation"  
>>> in HTTP
>>> sense might be.
>>> >From Xiaoshu's "I think there is no inherent relationship between  
>>> a representation and resource, let along
>>> isomorphic."
>>> ... to Pat's "But yes, I'm assuming that webarch:representation is  
>>> something like taking an imprint from a platen. It has to in some  
>>> sense be a 'faithful' representation of 'all' of the resource."
>>> Both of the above cannot be true, and allowing both interpretation  
>>> hurts
>>> web architecture. The HTTP spec provides no real guidance.
>>> I propose that the TAG provides the community with a single,  
>>> consistent
>>> view on this issue: "What is the relationship between a
>>> http:representation and a webarch:resource"?
>> Yes, I sincerely wish TAG would do this.  In addition I think TAG  
>> should also, as Pat proposed before, make an attempt to clarify the  
>> meaning of a few key words, such as "identify, denote, resource,  
>> thing, representation" etc.,
>> I am trying to put down my thought on the subject, once I did, I  
>> will post the URI as a source of argument.
>> Regards,
>> Xiaoshu
Received on Sunday, 25 November 2007 00:09:42 UTC

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