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Re: ACTION-983: same-document reference

From: Francois Daoust <fd@w3.org>
Date: Tue, 23 Jun 2009 13:11:02 +0200
Message-ID: <4A40B846.8020800@w3.org>
To: Jo Rabin <jrabin@mtld.mobi>
CC: Mobile Web Best Practices Working Group WG <public-bpwg@w3.org>
Well, the definition can be relied upon, can't it?

A Same Document Reference in a link element is an indication that this 
particular representation of the resource is mobile.
It can't be used to say that there exists a mobile representation of the 
resource at the same URI. Only "Vary" works in that case.

Again, that is just too bad, because we had an algorithm to make 
everything work if such a reference represented the resource and not 
this particular representation, but we come after the battle on that one 
as the definition would have to be changed in RFC3986.


Jo Rabin wrote:
> Well, I suppose not, but it means that the text needs to change to say that a same document reference in a link element can't be relied upon as an indication that the content is mobile. So we will have to take it out of the list or otehrwsie annotate it.
> Jo
>> -----Original Message-----
>> From: Francois Daoust [mailto:fd@w3.org]
>> Sent: 23 June 2009 07:46
>> To: Jo Rabin
>> Cc: Mobile Web Best Practices Working Group WG
>> Subject: Re: ACTION-983: same-document reference
>> Jo Rabin wrote:
>>> "Oh no!", the lemming says ...
>>>> [[
>>>>   the content is HTML and contains <link rel="alternate"
>>>> media="handheld" href="[same-ref]"/> where [same-ref] is a "Same
>>>> Document reference" as defined in RFC 3986 section 4.4 [REF]. In
>>>> particular, an empty href attribute is a "Same Document Reference".
>>>> ]]
>>> But this won't work for a multi-serving environment, will it. We are
>> left with only using a vary header in such situations?
>> That is right. It won't work for a multi-serving environment. That's a
>> shame, but we can't change the way the href attribute is understood for
>> our own purpose, can we?
>> Francois.
>>> Jo
>>>> -----Original Message-----
>>>> From: public-bpwg-request@w3.org [mailto:public-bpwg-request@w3.org]
>> On
>>>> Behalf Of Francois Daoust
>>>> Sent: 22 June 2009 16:43
>>>> To: Mobile Web Best Practices Working Group WG
>>>> Subject: ACTION-983: same-document reference
>>>> Hi,
>>>> Discussion on "same-document" references started a long time ago
>> when
>>>> Dom managed to have the group follow his unwise principle that a URI
>>>> always represents the resource and not a given representation of the
>>>> resource. This led to the production of a very smart algorithm in
>> the
>>>> last call version of the guidelines. This was shortly followed by
>> last
>>>> call comment LC-2009 [1]. The comment pointed us to section 4.4 of
>>>> RFC3986 "Uniform Resource Identifier (URI): Generic Syntax" [2] that
>>>> defines the concept of "same-document reference".
>>>> In particular, it does say:
>>>> [[
>>>>     When a same-document reference is dereferenced for a retrieval
>>>>     action, the target of that reference is defined to be within the
>>>> same
>>>>     entity (representation, document, or message) as the reference;
>>>>     therefore, a dereference should not result in a new retrieval
>>>> action.
>>>> ]]
>>>> ... meaning that a URI that appears in the representation of a
>> resource
>>>> and that happens to be a same-document reference represents the
>>>> representation of the resource, and not the resource itself.
>>>> We blamed Dom. We still had extensive discussions on the topic such
>> as
>>>> in [3], in particular because it also connects with the ("Oh no!",
>> the
>>>> Lemming says and explodes) ISSUE-222 [4] and the TAG Finding On
>> Linking
>>>> Alternative Representations To Enable Discovery And Publishing [5].
>> The
>>>> thing is the theory does not entirely match practice and most (all?)
>>>> browsers do not correctly handle the case when you want to use a
>>>> canonical URI for bookmarking purpose. Plus there is no true way to
>>>> define a URI as the canonical URI for a set of representations [6].
>>>> Whilst this is true, it is not directly related to the definition of
>> a
>>>> "same-document reference" and does not change its definition either.
>> In
>>>> short, unless we have good reasons not to, we should stick to the
>>>> definition of the above-mentioned RFC, and this is exactly what
>>>> Appendix
>>>> G.1.4.2 [7] does.
>>>> However, the first bullet point in section 4.2.9 [8] restricts the
>>>> possibility of a "Same Document reference" to an empty href
>> attribute.
>>>> For consistency, the text should rather be:
>>>> [[
>>>>   the content is HTML and contains <link rel="alternate"
>>>> media="handheld" href="[same-ref]"/> where [same-ref] is a "Same
>>>> Document reference" as defined in RFC 3986 section 4.4 [REF]. In
>>>> particular, an empty href attribute is a "Same Document Reference".
>>>> ]]
>>>> Francois.
>>>> [1]
>>>> http://www.w3.org/2006/02/lc-comments-tracker/37584/WD-ct-
>> guidelines-
>>>> 20080801/2009
>>>> [2] http://tools.ietf.org/html/rfc3986.html#section-4.4
>>>> [3] http://lists.w3.org/Archives/Public/public-bpwg-
>>>> ct/2008Sep/0027.html
>>>> [4] http://www.w3.org/2005/MWI/BPWG/Group/track/issues/222
>>>> [5] http://www.w3.org/2001/tag/doc/alternatives-discovery.html
>>>> [6] http://lists.w3.org/Archives/Public/public-
>> bpwg/2009Feb/0096.html
>>>> [7]
>>>> http://www.w3.org/2005/MWI/BPWG/Group/TaskForces/CT/editors-
>>>> drafts/Guidelines/090622#sec-use-of-link-element
>>>> [8]
>>>> http://www.w3.org/2005/MWI/BPWG/Group/TaskForces/CT/editors-
>>>> drafts/Guidelines/090622#sec-proxy-decision-to-transform
Received on Tuesday, 23 June 2009 11:11:36 UTC

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