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Re: [httpRange-14] Conneg and Acceptable HTTP Variants

From: Tim Berners-Lee <timbl@w3.org>
Date: Sat, 15 Dec 2007 14:41:34 -0500
Cc: www-tag@w3.org
Message-Id: <8DCF5993-63BC-41D5-9F27-35B70C473091@w3.org>
To: "Sean B. Palmer" <sean@miscoranda.com>


On 2007-12 -15, at 12:56, Sean B. Palmer wrote:

> Tim gave us a rule of thumb about what kind of HTTP variants it's
> acceptable to conneg between which caused some controversy:
> "When people conneg between HTML and RDF, the HTML is
> generated from the RDF. Else it is a bug." - TimBL, in [1]
> Dan Brickley was the first to cry wolf about this, asking how an
> acceptable level of degradation is defined. Kjetil Kjernsmo asked
> about a specific use case, of an RDF FOAF file generated from RDFa or
> What most of you may not have seen is that TimBL later gave Kjetil a
> very useful answer [2], which I repeat here:
> <timbl> kjetilkWork, re http://www.ski-o.com/user/kjetil you could
> offer both. Which would you want a person to see who is using
> FFox+Tabulator extension?
> <timbl> They won't get a chance to choose [...]
> <timbl> The user (a) is not going to know that two options exist if
> you use conneg and (b) is not going to be tweaking the q values of
> different file types as they click around the web.
> <timbl> Now I have the tab'r extension installed, occasionally I go to
> what I expected to be a useful web page but I get some RDF subset of
> it which doesn't work for me. As someone has thought conneg would be
> cute.
> I can testify that this is indeed annoying! The W3C site, for example,
> doesn't follow Tim's advice. Here's what I get when I try to request
> the W3C List Archives search interface:
> <?xml version="1.0" encoding="utf-8"?>
> <rdf:RDF xmlns:email="http://www.w3.org/2000/10/swap/pim/email#"
>    xmlns:log="http://www.w3.org/2000/10/swap/log#"
>    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>    xmlns:search="http://www.w3.org/Team/2001/09/search/search.pl#"
>    xmlns:session="http://dev.w3.org/cvsweb/perl/modules/W3C/Util/W3CDebugCGI.pm 
> ">
>    <rdf:Description rdf:about="" session:id="1197732779.352810"/>
> </rdf:RDF>
> - http://www.w3.org/Search/Mail/Public/search?type-index=www-tag&index-type=t
> That's not a satisfactory representation of the W3C List Archives'
> search interface. That is broken conneg. Conneg where, as Tim put it,
> someone thought conneg would be cute. The same thing applies to the
> FOAF specification: when I access that, I see the FOAF specification,
> which has *much* less information than the HTML specification.
> So the answer to the question of what is an acceptable level of A to
> A' degradation, i.e. the acceptable level of degradation between HTTP
> variants under conneg, is quite simple: if your users write you flames
> such as the paragraph above, you have gone too far!
> Tim's explanation to Kjetil compels me because not only is it easy to
> understand, but it's also grounded solely in use cases.
> (He turns out to be wrong, incidentally, that the HTML must be
> generated from the RDF, because you can devise an RDFa or GRDDL
> document where 99% or 100% of the content is contained in the RDF
> graph you get from it. But the intent is clear to me now.)
> [1] http://lists.w3.org/Archives/Public/www-tag/2007Dec/0035
> [2] http://chatlogs.planetrdf.com/swig/2007-12-05.html#T16-01-08
> -- 
> Sean B. Palmer, http://inamidst.com/sbp/
Received on Saturday, 15 December 2007 19:41:44 UTC

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