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Re: A possible design to incorporate collections and containers into RDFa? [ISSUE-16]

From: Ivan Herman <ivan@w3.org>
Date: Sun, 29 Aug 2010 10:25:43 +0200
Cc: W3C RDFa WG <public-rdfa-wg@w3.org>, Jeni Tennison <jeni@jenitennison.com>
Message-Id: <4878BB00-A3E7-4668-A6D0-D676A20B94E6@w3.org>
To: Toby Inkster <tai@g5n.co.uk>, Shane P McCarron <shane@aptest.com>

On Aug 28, 2010, at 22:51 , Toby Inkster wrote:

> On Wed, 25 Aug 2010 13:40:50 +0200
> Ivan Herman <ivan@w3.org> wrote:
>> I wrote down my current design on the Wiki:
>> http://www.w3.org/2010/02/rdfa/wiki/ContainersAndCollections
> I think this is a good start. Little problem though re the use of
> @resource to trigger the list behaviour. Consider the following:
> 	<div about="#eachpeach">
> 	    <i property="dc:title">Each Peach Pear Plum</i>
> 	    <ul rel="dc:creator" resource="::Bag">
> 	        <li property="::member">Janet Ahlberg</li>
> 	        <li property="::member">Allen Ahlberg</li>
> 	    </ul>
> 	</div>
> 	<div about="#megmog">
> 	    <i property="dc:title">Meg and Mog</i>
> 	    <ul rel="dc:creator" resource="::Bag">
> 	        <li property="::member">Helen Nicoll</li>
> 	        <li property="::member">Jan Pienkowski</li>
> 	    </ul>
> 	</div>
> If this were parsed in an RDFa 1.0 parser, it would come out as:
>  <#eachpeach>
>    dc:title "Each Peach Pear Plum" ;
>    dc:creator <./::Bag> .
>  <#megmog>
>    dc:title "Meg and Mog" ;
>    dc:creator <./::Bag> .
>  <./::Bag>
>    <http://www.w3.org/1999/xhtml/vocab#:member> "Janet Ahlberg" ;
>    <http://www.w3.org/1999/xhtml/vocab#:member> "Allen Ahlberg" ;
>    <http://www.w3.org/1999/xhtml/vocab#:member> "Helen Nicoll" ;
>    <http://www.w3.org/1999/xhtml/vocab#:member> "Jan Pienkowski" .
> Any automated agent looking at that would conclude that the two books
> have the same authors. Something using, say, @typeof wouldn't suffer
> from this problem.

I wonder, but I may be wrong. Is @resource="::Bag" legal? Didn't we say that for a relative URI to be really kosher one should do something like @resource="./XXX"? What I am trying to see if we can have the "trigger" strings ::Bag, ::member, etc, defined in such a way that they would be illegal if they stayed around on the RFDa level. I guess ::member is fine, because it cannot be interpreted as a term (it is not an NCNAME) and it is not an absolute URI. If we found the right strings that we would be safe. (I explicitly added Shane because he knows this better than everyone...)

But if there is no such string we may indeed have a backward compatibility issue in any case. Ie, if what we put into the attributes (both for @typeof or for @resource) is interpretable in RDFa 1.0 we could get to such problems. 

An easy way out is to define a separate attribute for these, something like parse_type (to borrow from the terminology used by RDF/XML). Ie, we could say that:

<span ... parse_type="Bag"> 

would generate the whole thing either by reusing an existing @resource or adding a new one with a blank node. That might have the added value (though rarely used in practice) to have a non-blank node acting as the rdf:Seq or the list header. But I was just a bit weary of adding a new attribute, though that may be the way to go.

As I said in my previous answer to Christoph[1] I feel there are too much problems reusing @typeof due to the additional and somewhat complex rules around it. I think it would scare away lots of users. Ie, I would prefer even accepting that corner case danger rather than creating a complex situation because of that corner case...



[1] http://lists.w3.org/Archives/Public/public-rdfa-wg/2010Aug/0173.html

> -- 
> Toby A Inkster
> <mailto:mail@tobyinkster.co.uk>
> <http://tobyinkster.co.uk>

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Sunday, 29 August 2010 08:23:44 UTC

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