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Re: RDFa DOM API Document update

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Tue, 18 May 2010 18:14:19 -0400
Message-ID: <4BF3113B.2060002@digitalbazaar.com>
To: RDFa WG <public-rdfa-wg@w3.org>
On 05/17/2010 03:17 AM, Toby Inkster wrote:
> On Sun, 16 May 2010 21:50:18 -0400
> Manu Sporny <msporny@digitalbazaar.com> wrote:
> 
>> http://www.w3.org/2010/02/rdfa/sources/rdfa-dom-api/Overview-src.html
> 
> How exactly do these getElementsByX methods work? Although RDFa defines
> how to generate an RDF graph from a DOM tree, it doesn't offer a clear
> and unambiguous mapping back from the RDF graph to DOM nodes.

Right, we'd have to specify how that mapping happens.

I was thinking about something along these lines:

* The active DOM node is carried along with the context
* When a subject, predicate or object starts to be generated, the
  currently active DOM node is associated with the subject, predicate
  or object being created.

> For example:
> 
> 	<a about="#me" typeof="foaf:Person"
>            rel="foaf:homepage" href="http://example.com/">
> 	  <span rel="rdf:type" resource="[foaf:Document]"
> 	     property="dc:title">My Homepage</span>
> 	</a>
> 	<i about="#me" property="foaf:name">Joe</i>
> 
> What element would be returned in the case of
> getElementsByType('foaf:Person')? Presumably the <a> element because it
> set the subject for the {?thing rdf:type foaf:Person} triple.

Yes, it would be where the @typeof is specified - or rather, the subject
("#me"), the predicate (rdf:type), and the object (foaf:Person) would
all have the same ".origin" property - the <a> Element.

> But what about the getElementsByType('foaf:Document')? If we apply the
> same reasoning, it would be the <a> element too.

Well, if we apply the "currently active node" rule for determining the
associated DOM Node, it would be the currently active node when the
object was determined, in this case, the <span> tag. So the triple's DOM
Node associations would be:

subject   -> "#me"         -> <a>
predicate -> rdf:type      -> <span>
object    -> foaf:Document -> <span>

> Would the <i> element be selected by getElementsByType('foaf:Person')?
> After all, we know #me is a foaf:Person.

Nope, getElementsByType() only returns DOM Elements that are directly
associated with the declaration of that type. So, only these patterns
would match:

@typeof
@rel w/ @src/@href/@resource

Even when we get fancy, I think this works:

<div rel="rdf:type">
   <span resource="foaf:Document" />
   <span resource="sioc:Post" />
   <span resource="owl:Thing" />
</div>

In each case about getElementsByType() would return the associated span
element for foaf:Document, sioc:Post, and owl:Thing.

> As much as I think these getElementsByX methods would be useful, I
> don't think they can be implemented in an especially obvious,
> consistent and predictable way.

Does this approach change your mind? It's a fairly simple rule, can you
think of where it may break down?

-- manu

-- 
Manu Sporny (skype: msporny, twitter: manusporny)
President/CEO - Digital Bazaar, Inc.
blog: Bitmunk 3.2.2 - Good Relations and Ditching Apache+PHP
http://blog.digitalbazaar.com/2010/05/06/bitmunk-3-2-2/2/
Received on Tuesday, 18 May 2010 22:14:48 GMT

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