Re: Official Response to ISSUE-121 from RDF Web Apps WG

Sebastian,

as far as I am concerned there is a major issue with the usage of @id, and that is backward compatibility with RDFa 1.0. Manu referred to that in his mail, but maybe it was not emphasized enough. Although the charter allows us to introduce backward incompatibilities with RDFa 1.0 when there are very compelling reasons for this (and we did introduce some), it also instructs us to be very careful about this.

If I look at 

<div id="a" typeof="q:r" >

The RDFa 1.0 specification clearly states that the result is the creation of a blank node, that gets the type 'q:r', and that becomes the subject for the tree underneath <div>. If your proposal was accepted, the resulting graph would be significantly different insofar as the node would not be a blank node any more but <#a>.

Because @id is a valid and widely used HTML attribute, whose usage is dictated by very different goals than RDF(a), such patterns might be very widespread in the wild. I do not believe the Working Group should make such a strong backward-incompatible change that might invalidate or significantly change a large number of existing RDFa pages.

Ivan



On Jan 30, 2012, at 03:49 , Sebastian Heath wrote:

> Hi Manu,
> 
>  The discussion in the teleconference[1] isn't very complete but
> suggests there is reason to keep this issue alive.
> 
> GK wrote "it's always been something I would've liked, my primary use
> case for RDFa is for legal information, where we refer to document
> fragments more often than not."
> 
> NL wrote " (.. the 0.05 is for my dream of a good working solution ;)".
> 
> The above suggests the idea is worth pursuing.
> 
> And there isn't much for me to respond to in the official reply as
> it's somewhat vague.
> 
> 
>> 1. There are a slew of non-trivial HTTP-Range-14 issues about which
>>   namespace @id refers to and which namespace @about refers to that
>>   would be raised. Document identifiers mixing with semantic item
>>   identifiers would be problematic at best.
> 
> "slew" is not very specific and so hard for me to respond to. I would
> welcome more detail. In general, I believe the tenor of my response is
> that a very flexible definition of "resource" lies at the core of RDF
> (see for example the range of rdfs:isDefinedBy) but I hesitate to
> write more in this direction without more specificity from the WG.
> HTTP-Range-14 issues come up in some contexts, but by no means all and
> so their simple invocation is inconclusive.
> 
>> 2. It would break existing documents that use @typeof and @id on the
>>   same document.
> 
> A simple versioning mechanism for RDFa in XHTML would solve this.
> 
>> 3. It would make RDFa more complicated than it already is.
> 
> How? For the use cases I suggest[2], it would make things simpler.
> 
>> 4. There are no compelling use cases - that is, most use cases can
>>   already be addressed using the attributes that exist right now.
>> 
> 
> I offered 2 in a further comment [2] but it seems they weren't
> addressed. Or I should say I offered two cases that were compelling to
> me. GK added what might be considered another.
> 
> So to be clear, I consider the issue still open and not fully
> discussed. Many changes have been made to RDFa in the last few months
> to ease its adoption and I think ISSUE 121 warrants further
> discussion.
> 
> Thank you,
> 
> Sebastian.
> 
> 
> [1] http://www.w3.org/2010/02/rdfa/meetings/2011-12-08#ISSUE__2d_121__3a__Use___40_id_to_set_the_subject_in_RDFa
> [2] http://lists.w3.org/Archives/Public/public-rdfa-wg/2011Nov/0149.html
> (the formatting of this seems to have gone wrong so I can resend.)
> 
> On Sat, Jan 28, 2012 at 1:47 PM, Manu Sporny <msporny@digitalbazaar.com> wrote:
>> Hi Sebastian,
>> 
>> Thank you for your public feedback on the RDFa 1.1 documents. This is an
>> official response from the RDF Web Apps WG to your issue before we enter
>> the 3rd Last Call for the RDFa 1.1 work this coming Tuesday. The Last
>> Call will last for 3 weeks, so there is still time for you to discuss
>> your concerns if we have not fully addressed them.
>> 
>> Your issue was tracked here:
>> 
>> ISSUE-121: Using @id to set subject in RDFa
>> https://www.w3.org/2010/02/rdfa/track/issues/121
>> 
>> Explanation of Issue
>> --------------------
>> 
>> You had wanted us to consider allowing @id attribute to set the subject
>> when @typeof existed on the same element:
>> 
>> """
>> Currently, RDFa processors do not take account of @id attributes in
>> host-languages. In particular, in (x)html the @id attribute is
>> ignored. In (x)html, this creates unnecessary complication in which
>> the value in @id needs to be prefixed by '#' and put in an @about
>> attribute in order to make semantic markup visible to both html agents
>> and rdfa processors.
>> 
>> Example:
>> 
>>  <p id="item1" typeof="ex:item" about="#item1">
>>   <span property="item_name">An interesting item (1)</span>
>>  </p>
>> 
>> I suggest that a combination of @typeof and @id cause the subject to
>> be set to the fully qualified URL implied by the value @id, according
>> to normal URL processing rules defined for HTML and related languages.
>> """
>> 
>> Working Group Decision
>> ----------------------
>> 
>> The Working Group had considered allowing this very early in the RDFa
>> 1.0 days and decided that @id by itself would generate far too many junk
>> triples in the output. We re-opened the issue because we did not believe
>> that we had discussed @typeof and @id being used in concert to create a
>> triple. The full discussion can be found here:
>> 
>> http://www.w3.org/2010/02/rdfa/meetings/2011-12-08#ISSUE__2d_121__3a__Use___40_id_to_set_the_subject_in_RDFa
>> 
>> The WG felt that the following issues prevent us from adopting what you
>> propose:
>> 
>> 1. There are a slew of non-trivial HTTP-Range-14 issues about which
>>   namespace @id refers to and which namespace @about refers to that
>>   would be raised. Document identifiers mixing with semantic item
>>   identifiers would be problematic at best.
>> 2. It would break existing documents that use @typeof and @id on the
>>   same document.
>> 3. It would make RDFa more complicated than it already is.
>> 4. There are no compelling use cases - that is, most use cases can
>>   already be addressed using the attributes that exist right now.
>> 
>> So, in the end, the WG did the following:
>> 
>> RESOLVED: The @id attribute MUST NOT be used to identify a subject in RDFa.
>> 
>> http://www.w3.org/2010/02/rdfa/meetings/2011-12-08#resolution_4
>> 
>> Feedback
>> --------
>> 
>> Since this is an official Working Group response to your issue, we would
>> appreciate it if you responded to this e-mail and let us know if the
>> decision made by the group is acceptable to you as soon as possible.
>> 
>> -- manu
>> 
>> --
>> Manu Sporny (skype: msporny, twitter: manusporny)
>> Founder/CEO - Digital Bazaar, Inc.
>> blog: PaySwarm vs. OpenTransact Shootout
>> http://manu.sporny.org/2011/web-payments-comparison/
> 


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