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Re: Reification support in RDFa

From: Elias Torres <elias@torrez.us>
Date: Mon, 16 Oct 2006 23:18:41 -0400
Message-ID: <45344B91.8080100@torrez.us>
To: Dan Connolly <connolly@w3.org>
CC: public-rdf-in-xhtml task force <public-rdf-in-xhtml-tf@w3.org>



Dan Connolly wrote:
> On Mon, 2006-10-16 at 17:32 -0400, Elias Torres wrote:
>> During today's meeting we were discussing our current support for RDF
>> reification in our current syntax draft [1] which states:
>>
>> [[[During subject resolution (which could be triggered by object
>> resolution for a rev attribute), the processor may traverse up the DOM
>> tree in search of an about  attribute. If a link or meta element is
>> encountered before an about attribute is found, and if this link or meta
>> element itself does not have an about attribute, then the subject (or,
>> again in the case of rev, object) is resolved as the [RDF/A statement]
>> represented by this link or meta  element.]]]
> 
> I'm not fond of specifying meaning of documents in terms
> of behavior of software ("the processor may...") but the example
> that followed makes it pretty clear what's going on; and what's
> going on falls completely within RDF as specified in the 2004
> Recommendations. The turtle output is completely ordinary RDF:
> 
>  <> cc:license <http://creativecommons.org/licenses/by-nc-nd/2.5/> .
>  <> dc:creator "Mark Birbeck."  
>  _:a rdf:type rdf:Statement .
>  _:a rdf:subject <> .
>  _:a rdf:predicate cc:license .
>  _:a rdf:object <http://creativecommons.org/licenses/by-nc-nd/2.5/> .
>  _:a dc:creator "Ben Adida" .
> 
> 
>> The main discussion point was who are the folks (such as IPTC and others
>> from HTML WG) asking for reification and what the real requirement is
>> for RDFa. Additionally, I brought up the point that the reification [2]
>> vocabulary is not either clearly defined, implemented or used today and
>> that we must be careful on taking on such a task.
> 
> I think it's reasonably well defined. It does not meet quoting
> requirements, but the example in this RDFa draft doesn't involve
> real quoting.

That's correct. The example in the syntax document is the classic RDF
reification definition: Ben said a statement with the following s,p,o.

> 
> 
>>  Reification in RDF M&S
>> leans towards identification of statements as opposed to quotation [3].
>> It's not clear which one we want in RDFa.
> 
> I don't see anything that suggests you want quotation. What
> am I missing?

Maybe you are not missing anything and I just did a poor job of
summarizing the issue for the mailing list (which was my action during
the meeting) and instead clouded the issue. But at least we had another
pair of eyes to look at it.

Besides the id/quote issues in reification, I believe is still to be
resolved what do we name the statements themselves. M&S says that the
identifier should identify a specific triple instance in an RDF document
and we don't necessarily have an RDF document, Named Graph, etc. Do you
think that this is an issue?

Another small issue is that an element could generate N number of
statements (rel, rev, property, + multi-value rel/rev attribute values)
and we haven't discussed whether a reification property applies to all
of those statements. When I say we don't know the exact requirement is
whether we are looking to give provenance on the HTML element or on a
specific RDF triple generated from the HTML (i.e. Ben added the @rel
value, but Mark added @rev). Can we distinguish between those two? Do we
need to? It seems to me that if we are going to define how to add
provenance to HTML documents/fragments we must address this question.


> 
>> I'd like for us (everyone) to discuss more how do we really want to
>> approach reification in RDFa, especially since we have a better
>> situation due to us dealing with HTML documents. We have documents being
>> published on the web at specific locations and I think we have different
>> two major ways to frame the issue/requirement. We might want to track
>> provenance at the HTML/element level (e.g. who wrote what piece of HTML)
>> vs at the RDF level (who said which triple). I think one option is for
>> us to establish our purpose and provide a specific vocabulary to do so
>> without dragging the whole use/mention, bnodes, named graphs issues
>> attached with RDF reification and the communities trying to resolve it.
>>
>> Any thoughts?
> 
> The relevant requirement for me is that RDFa be convertible to RDF/XML;
> i.e. no more expressive. Real quoting would involve going beyond
> the existing expressive capability of RDF/XML.

k. requirement noted and we need to make sure we don't step out of the
realm of what's doable in RDF/XML (e.g. generate invalid XML names).

> 
> But I don't see anybody arguing for that.
> 
>> -Elias
>>
>> [1]
>> http://www.w3.org/2001/sw/BestPractices/HTML/2005-rdfa-syntax#id0x01cc64a0
>> [2] http://www.w3.org/TR/rdf-primer/#reification
>> [3] http://ioctl.org/rdf/usementionmyarse
Received on Tuesday, 17 October 2006 03:18:58 GMT

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