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Re: Alternative to 303 response: Description-ID: header

From: Tim Berners-Lee <timbl@w3.org>
Date: Wed, 5 Dec 2007 10:31:11 -0500
Cc: "Sean B. Palmer" <sean@miscoranda.com>, David Booth <dbooth@hp.com>, www-tag@w3.org
Message-Id: <304A3A93-1FC9-427F-94D1-34F1678F8AEA@w3.org>
To: Ian Davis <lists@iandavis.com>


Your blog says, in http://iandavis.com/blog/2007/12/303-asymmetry

'Suppose I have a resource “R” with URI http://example.org/R. If it is  
an “Information Resource” then I can arrange things so that a GET  
request for its text/html representation responds with a 200 and the  
HTML in the body of the response. I could also arrange for a request  
for its application/rdf+xml representation to respond with a 303  
status and the URI of another information resource “RDESC” (e.g. http://example.org/RDESC) 
. In this example the 303 response meand that “R” cannot be  
represented as RDF, but there’s an alternative RDF document that is a  
description of R."

There is a major problem with this, though.   Content negotiation is  
just for different encodings of the SAME document.
You can content negotiate between PNG and JPG of the SAME picture.
Between text/plain and text/html of the SAME document.
Between RDF/xml and N3 of the SAME data.

You cannot use conneg to return a completely different document, eg  
not A but  metadata bout A.
A and A' must carry exactly the same information, module an  
'acceptable' degree of degradation.

When people conneg between HTML and RDF, the HTML is generated from  
the RDF. Else it is  a bug.

You say, "How can I allow the user to obtain a description of RDESC?  
The representation I send back is the content of RDESC, not its  
description. I can’t use the media type to distinguish the type of  
request any more."
Sorry, you never could.

The resource-description header you suggest seems very similar to teh  
HHP link header, Link: foo.rdf; rel=meta
(se http://esw.w3.org/topic/LinkHeader)


On 2007-12 -04, at 20:56, Ian Davis wrote:

> On Tue, 2007-12-04 at 19:53 -0500, Tim Berners-Lee wrote:
>> I did wonder about the following:  in the case when the URI is not of
>> document, when currently we use 303,
>> then the  server can return a document *about* it with  an extra
>> header to explain to the browser
>> that it is actually giving you a description of it not the content of
>> it.  (Pick a header name)
> Strange synchronicity... I posted the same idea a few minutes ago to  
> my
> blog:
> http://iandavis.com/blog/2007/12/303-asymmetry
> I called my header "resource-description"
> Ian
Received on Wednesday, 5 December 2007 15:31:23 UTC

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