Re: Some thoughts on the RDFa DOM API document

On Apr 27, 2010, at 11:47 , Toby Inkster wrote:

> On Tue, 27 Apr 2010 09:42:32 -0400
> Manu Sporny <msporny@digitalbazaar.com> wrote:
> 
>> Good catch, Benjamin... I wonder why Blank Nodes aren't allowed as
>> predicates?
> 
> It's a bit of an annoying restriction. A lot of N-ary relationship
> problems could be solved by bnode predicates. e.g. 
> 
> 	<#school>
> 		[
> 		  rdfs:subPropertyOf teaching:teacher ;
> 		  teaching:subject thesaurus:Maths ;
> 		  rdfs:label "maths teacher"@en
> 		]
> 			<#joe> .
> 
> N3 allows blank node predicates; the SPARQL query language does too
> (though pretty much all SPARQL engines sit on top of RDF quad or triple
> stores, so in practice they never get a chance to see any bnode
> predicates). RDF doesn't though. Along with literal subjects, it's an
> oft-mentioned wishlist item for a future version of RDF should there
> ever be one.
> 
> TimBL noted that blank node predicates would be useful when he reviewed
> the RDF Concepts & Abstract Data Model:
> <http://www.w3.org/2002/07/29-rdfcadm-tbl.html#xtocid48022>.
> 
> So, while RDF doesn't allow bnode predicates, we should bear in mind
> that a future version of RDF might. This means that while RDFa and the
> DOM API shouldn't allow bnode predicates, we should try to avoid making
> decisions that would make it difficult to add that feature in a future
> version.

Very much so. Actually, not having bnodes as properties does create problems for reasoners, too, as well as mapping some OWL constructs to RDF. I would expect a new version of RDF removing this restriction, so we should not do anything that would create difficulties later... And there is an RDF Next workshop coming up that may end up with an RDF Working Group...

Ivan


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


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Ivan Herman, W3C Semantic Web Activity Lead
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