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HT's notes on conneg for TAG meeting

From: Dan Connolly <connolly@w3.org>
Date: Tue, 03 Mar 2009 09:59:53 -0800
Message-ID: <49AD7019.7070202@w3.org>
To: ht@w3.org, www-archive@w3.org
capturing for the meeting record what was in 

1. Conneg.
1.1. Review of the thread

Hausenblas asks

     "is the PNG *representation* derived via conneg from the generic 
resource <http://sw-app.org/sandbox/house> equivalent to the RDF in Turtle?"

Two possible answers:

    1. Yes, because you own the resource and by doing the conneg that 
way you are asserting that they are equivalent for your purposes
    2. But you are being unhelpful in asserting that equivalence, as it 
is unhelpful to users. The png response implies the resource is an IR, 
i.e. that the generic URI identifies "an image of a house". The RDF 
response (modulo the lack of redirection) implies the resource is not an 
IR, i.e. that the generic URI identifies a house.

The overloading of conneg to attempt UAM is bad for web architecture, 
but the correct response is to provide a clean UAM story, which should 
relieve the pressure on conneg.

[The Williams/Davis exchange is a red herring, IMO]

[The OP was not asking about entity tags, but about

WebArch itself talks mostly about 'consistency', including the 
intriguing line "Improper use of content negotiation can lead to 
inconsistent representations." C.f. JAR's 0170, I think webarch's 
comments on CN are all contextualised by an assumption that we're 
talking about png vs. jpg or 1200x1600 vs 600x800.

Xiaoshu's 0105 is interesting, in that it raises well the issue of what 
the resources are that are named by the URIs returned as 
Content-locations: in responses to conneg. Do we have an answer to this 
one? In Raman's alternatives discovery finding? Hmmm, yes, he talks 
about 'generic resources' and 'specific resources' as if they were 
distinct. . . Language conneg, UA-type conneg (VARY?) and Content-type 
conneg are possibly different in this regard?

My top-of-my-head response is that all three URIs identify the same 
resource. I think we're forced to that conclusion by the fact that the 
owner asserts that both representations are representations of the 
resource identified by the original URI. . . Can the current state of 
AWWSW prove this conclusion?

JAR's narrative in his 0172 makes me uncomfortable, and what it is that 
makes me uncomfortable is precisely the possibility of two things which 
are so different as PNG and RDF being served as alternatives. . . I am 
inclined to reject even the "PNG of the graph" or "graph of the pixels" 
2nd-order thought experiments, because what's crucial wrt Media Types is 
that applications which understand that media type will produce 
consistent effects. In none of the three cases is that true.

Last-minute thread

Axiom 1 is true with or without frag-ids. . .

I don't think Axiom 2 is correct. . .

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 3 March 2009 17:59:42 UTC

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