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Re: opaque uris and self-describing resources

From: Michaeljohn Clement <mj@mjclement.com>
Date: Fri, 18 Jan 2008 07:32:32 -0700
Message-ID: <4790B880.90409@mjclement.com>
To: "Clive D.W. Feather" <clive@demon.net>, URI <uri@w3.org>

Erik Wilde wrote:
>>> so i assume to discover the non-http nature of the resource 
>>> identified by u1, there must be some content within the returned 
>>> resource that makes that statement. logically, i see three ways how the 
>>> non-httpness of the identified resource could be established:
>>> 1. string matching with a magic prefix
>>> 2. the 303 returned when dereferencing the uri
>>> 3. embedded metadata in the returned resource

Sandro Hawke wrote:
>> The TAG reached consensus on 15 Jun 2005 to use option 2.

That is not my understanding of the consensus that was reached.

What I understood the TAG resolution to say is that the 303 implies 
only the *possibility* that the resource might be something other than 
an information resource.  The 303 does not indicate that the resource 
*is not* an information resource.  (What I think Erik meant by 

The 303 approach gives you a way to use HTTP URIs for non-information 
resources, and it gives you a way to dereference those URIs and find 
related information, but it does not give you a way to unambiguously 
declare, merely by a status code, that that an HTTP URI identifies a 
non-information resource.  (It also doesn't retroactively declare all 
existing 303-returning resources to be non-information resources, 
which would clearly be a mistake.)

If that's the case, then you can't at all get from a 303 to Erik's 
"non-httpness of the identified resource".  For that you would need 
option 3, option 1, or some other out-of-band information.

Clive D.W. Feather wrote:
> How does this work when I'm not online? How does my software discover that
> there's something special about this URL?

If I'm correct above, your software can't discover that by merely 
doing a GET even when you are online, so there is no change.

Michaeljohn Clement
Received on Friday, 18 January 2008 14:33:46 UTC

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