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Re: Subgroup to handle semantics of HTTP etc?

From: Richard Cyganiak <richard@cyganiak.de>
Date: Mon, 22 Oct 2007 18:53:09 +0200
Message-Id: <431D43F9-E449-4E8E-9D3D-77E3570E942B@cyganiak.de>
Cc: www-tag@w3.org, Alan Ruttenberg <alanruttenberg@gmail.com>, Dan Connolly <connolly@w3.org>, "Booth, David (HP Software - Boston)" <dbooth@hp.com>, Jonathan A Rees <jar@mumble.net>, "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, Tim Berners-Lee <timbl@w3.org>
To: wangxiao@musc.edu

Xiaoshu,

On 22 Oct 2007, at 16:56, Xiaoshu Wang wrote:
> I think from this wording in AWWW - "The distinguishing  
> characteristic of these resources is that all of their essential  
> characteristics can be conveyed in a message", the implication, at  
> least for me, is that "from the representation of an information  
> resource, we can *fully* understand the resource".

I wouldn't read that much into the definition. The definition does  
not even require that there actually *is* a representation associated  
with the resource, just that there *could* be one, in theory.

> The point that I want to stress is: from a particular  
> representation, you can only know *a part* of what the URI  
> identifies and we cannot tell how big the part is from its URI or  
> its network response code.
> This, in my opinion, makes the distinction between IR and non-IR  
> pointless.

The point is that it partitions resources into two kinds: message- 
conveyable resources, and other resources. And it establishes an  
axiom, that a 200 response means we have a message-conveyable resource.

This axiom might seem somewhat arbitrary, but it has huge practical  
implications. Thanks to this axiom, a terrible uncertainty about the  
meaning of almost every URI on the current Web simply disappears.

Without this axiom, it is not clear wether the URI of my homepage  
identifies just a document, or wether it can be also used to identify  
a person. This uncertainty exists for almost every web page. The  
axiom removes any doubt: The answer is 200, therefore the URI  
identifies something message-conveyable, therefore it cannot be a  
person, therefore it must identify just the document.

The value of httpRange-14, in my eyes, is simply this: It affirms  
that web page URIs still identify web pages, even in the Semantic Web.

> Because as you said, the relationship between representation and an  
> information resource is not one-to-one. Thus, if we cannot tell how  
> much the "representation" represents the "information resource",  
> then how to differ an IR from a non-IR? Then, who should get 303  
> and who should not?

I like the "Halpin Test" [1]:

"I would say that if there is a URI that is used to identify a  
resource one would want to make logical statements about, and these  
statements do not apply to possible representations of that resource,  
then one should use the "hash" or 303 redirection to separate these  
URIs."

To me, that's good enough as an every-day sniff test.

Best,
Richard

[1] http://lists.w3.org/Archives/Public/www-tag/2007Sep/0123.html


>
> Xiaoshu
>
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Received on Monday, 22 October 2007 16:53:40 UTC

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