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Re: order within a @prefix

From: Ivan Herman <ivan@w3.org>
Date: Thu, 2 Dec 2010 13:33:00 +0100
Cc: Shane McCarron <shane@aptest.com>, Toby Inkster <tai@g5n.co.uk>, W3C RDFa WG <public-rdfa-wg@w3.org>
Message-Id: <8D219E09-38B2-46D8-BC64-2F0A34D16443@w3.org>
To: Mark Birbeck <mark.birbeck@webbackplane.com>
Mark,

to be absolutely honest with you: I do not care. This is a typical edge case; no author in his/her able mind would do this anyway. But an implementation has to know, so we need a resolution. If we want to make use a virtual coin, that can also work...

Ivan



On Dec 2, 2010, at 13:14 , Mark Birbeck wrote:

> Hi Ivan,
> 
> I guess in one sense left-right v. right-left doesn't make much
> difference. However, our processing rules generally have a sort of
> 'later overrides earlier' aspect to them, based on the hierarchical
> nature of the documents that we're parsing. Having a rule where the
> deeper nodes override their parents' values makes processing very
> easy.
> 
> Now, of course you could say that 'latest wins' would still be the
> rule inside the @prefix attribute if we processed from right to left.
> But I do think that would be a little odd, given that conventionally
> people see the DOM hierarchy as going from left to right.
> 
> To illustrate, our processing model would say that the second
> occurrence of 'foaf' in this example applies due to the hierarchy (in
> a sense, it's 'later overrides earlier'):
> 
>  <div prefix="foaf: http://blah1">
>    <div prefix="foaf: http://blah2">
>      <!-- use blah2 --->
>    </div>
>  </div>
> 
> Writing an example where the same prefix is defined in @prefix might
> look like this:
> 
>  <div prefix="foaf: http://blah1
>                    foaf: http://blah2">
>      <!-- should really use blah2 --->
>    </div>
>  </div>
> 
> I think it would be counterintuitive if the left-most prefix was
> preferred over the right-most one, in this example.
> 
> This simplicity of overriding is lost in the processing of profiles
> (as a result of the resolution you refer to on ISSUE-23). The way that
> the processing is now described in section 9 implies that you need to
> track each profile loaded to see if there is a conflict later. Of
> course, the easiest way to implement this is to process from right to
> left, which removes the need to track each profile, but then I think
> most implementers will rightly ask...why is everything else going from
> left to right, except @profile?
> 
> We know that the only reason profile processing was made to work from
> right to left was due to the legacy use of @profile, in which only the
> first value had significance; some argued that this implied that the
> left-most profile should be the most important, and therefore should
> override others.
> 
> Personally, I didn't find this very convincing (and the resolution
> didn't have great support), but we have the resolution now.
> 
> However, given that we have the resolution to deal with a legacy
> issue, it should really be regarded as an anomaly, I it certainly
> shouldn't be used as a model for other processing rules.
> 
> Regards,
> 
> Mark
> 
> 
> On Thu, Dec 2, 2010 at 9:56 AM, Ivan Herman <ivan@w3.org> wrote:
>> Shane,
>> 
>> there is no separate comment list; the reference in the document for comments is the WG mailing list...
>> 
>> But yes, this _is_ a last call comment, though I thought it is an editorial issue.
>> 
>> So, to make it clear, the question is what is the effect of @prefix="a: http://a.b a: http://c.d". In my original mail I said it should be left to right. But I since seemed to remember that we decided to have it right to left, ie, in my example, the result should be a->http://a.b. I tried to find a resolution in the mail archives, but I could not. However I did find this:
>> 
>> http://lists.w3.org/Archives/Public/public-rdfa-wg/2010May/0123.html
>> 
>> which led to a discussion thread on the relative priority within a @profile. This led to this resolution:
>> 
>> http://www.w3.org/2010/02/rdfa/meetings/2010-06-03#resolution_7
>> 
>> ie, left-most declaration wins. I have not found any resolutions related to @prefix. However, based on the the resolution we have already taken for @profile I would propose to define the same order for @prefix and that should be documented in RDFa 1.1 Core
>> 
>> Ivan
>> 
>> 
>> 
>> 
>> On Dec 2, 2010, at 02:01 , Shane McCarron wrote:
>> 
>>> Since we are in last call, please submit this as a last call comment to the appropriate public list before the deadline.
>>> 
>>> On 12/1/2010 6:16 PM, Toby Inkster wrote:
>>>> On Wed, 1 Dec 2010 11:21:55 +0100
>>>> Ivan Herman<ivan@w3.org>  wrote:
>>>> 
>>>>> @prefix="a: http://a.b a: http://c.d"
>>>>> 
>>>>> will end in a->http://c.d
>>>>> 
>>>>> However, I tried to locate this in the document and I could not...
>>>> That's what I do, but I agree we need to make this explicit as it's a
>>>> case that implementors will definitely need to handle.
>>>> 
>>> 
>>> --
>>> Shane P. McCarron                          Phone: +1 763 786-8160 x120
>>> Managing Director                            Fax: +1 763 786-8180
>>> ApTest Minnesota                            Inet: shane@aptest.com
>>> 
>>> 
>> 
>> 
>> ----
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> mobile: +31-641044153
>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>> FOAF: http://www.ivan-herman.net/foaf.rdf
>> 
>> 
>> 
>> 
>> 
>> 


----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf







Received on Thursday, 2 December 2010 12:30:42 UTC

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