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

On Mon, 18 Jan 2010, Philip Jägenstedt wrote:
> 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?

Looped references are one of the features that were explicitly deferred to 
the next version, because there simply weren't use cases that needed it. I 
designed the mechanism that one would use to do it back when first writing 
the Microdata section, I just didn't include it.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'