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

From: <noah_mendelsohn@us.ibm.com>
Date: Wed, 5 Dec 2007 00:18:43 -0500
To: Tim Berners-Lee <timbl@w3.org>
Cc: "David Booth" <dbooth@hp.com>, "Sean B. Palmer" <sean@miscoranda.com>, www-tag@w3.org
Message-ID: <OFFC6331C6.DC275D98-ON852573A8.0015F616-852573A8.001790B7@lotus.com>

Tim Berners-Lee writes:

> 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)

Me too.  In fact, I've wondered since I first became aware of the 
httpRange-14 fuss why this wasn't a good answer, and assumed there must be 
some deep reason it wasn't OK.  You then wrote:

> The disadvantage is that if you ignore the header you get a semantic
> inconsistency, 

If that's the concern, it doesn't seem too bad to me at first blush.  I 
continue to think the header approach is promising.

> but well, those people who are concerned about such things could [...]

Something missing and the end there, but I presume you meant "could use a 
suitable client that would understand the header."  Yes.

One followup question.  You proposed above a header that would warn of 
returned entities that are "about" the resource originally requested.  I 
wonder whether it's worth distinguishing among 3 cases:

Case 1:  today's 200 -- this is a "representation" of an IR
Case 2:  it's a (necessarily) very imperfect and incomplete representation 
(choose your favorite alternate noun) of a resource that's not an IR.  For 
example, the URI designates "Noah", and what comes back is an image/jpeg 
with a photograph of me.  It does "represent" me in a sense, but not the 
sense we've meant so far in AWWW.
Case 3:  it's "about" the resource (Noah is employed by IBM)

I infer that you are proposing not to distinguish cases 2&3, but with a 
header we easily could.  Is distinguishing cases 2 and 3?  I could imagine 
browser-type user agents that, as a matter of policy, would directly 
display the image from case 2 with UI quite similar to what you'd use in 
case 1.  I'd expect different UI for case 3.  I'm not sure whether this 
distinction is worth pursuing, or just unnecessary complexity that will 
confuse users.  I still think there are a lot of people out there who 
think that a picture is a plausible, if incomplete, "representation" of a 
person, and would be happy to see it when following a link to "me", 
especially since the browser could in small print say something along the 
lines of "You've linked to a resource that is not a document--what you're 
seeing is a page that's intended to depict the resource you asked for."  I 
don't think I'd do that for a page that said "Noah is employed by IBM." 
That doesn't depict me at all.

Anyway, either way, I like the overall suggestion to think more about 
using headers.

Noah



--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
--------------------------------------
Received on Wednesday, 5 December 2007 04:17:25 GMT

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