Re: The harm that can come if the W3C supports publication of competing specs

On Sun, 17 Jan 2010 20:47:29 +0100, Toby Inkster <tai@g5n.co.uk> wrote:

> Cyclical references amongst blank nodes cannot be represented in
> Microdata. In Turtle an example might be:
>
> 	@prefix foaf: <http://xmlns.com/foaf/0.1/> .
> 	_:bob foaf:knows _:jon .
> 	_:jon foaf:knows _:bob .
>
> In RDFa it can be expressed quite simply:
>
> 	<p xmlns:knows="http://xmlns.com/foaf/0.1/knows"
> 	   about="_:jon" rel="knows:" rev="knows:" resource="_:bob">
> 	  Jon and Bob know each other.
> 	</p>
>
> To express the same semantics in Microdata would require assigning a URI
> to at least one of the people. Certainly it's possible for a script to
> assign a URI on the fly, but committing to maintaining the meaning of
> that URI long-term is harder, which is why blank nodes are so frequently
> used in RDF.
>
> I believe, this could be addressed by allowing @itemid to contain a
> blank node name, and providing a way for @itemprop to specify a blank
> node as its value.

Right, if there's an actual need then it's easy to hardwire the _:foo  
syntax to create blank nodes in the RDF extraction algorithm. Currently  
the algorithm ignores item types which aren't absolute URIs. Is _:foo an  
absoute URI, or is it not a URI at all?

-- 
Philip Jägenstedt
Core Developer
Opera Software