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Re: W3C specification error

From: Dan Brickley <danbri@w3.org>
Date: Mon, 29 Nov 2004 15:25:19 -0500
To: Pat Hayes <phayes@ihmc.us>
Cc: Andrea Proli <aprol@tin.it>, www-rdf-comments@w3.org
Message-ID: <20041129202519.GH20326@homer.w3.org>

* Pat Hayes <phayes@ihmc.us> [2004-11-29 14:14-0600]
> >Thanks, I'll take a look. I remember (dimly!) the group making some 
> >decision on
> >this which seemed counter-intuitive. I've copied www-rdf-comments to put
> >your note on the record, hope that's OK. I think what happened might be
> >that the mathematics of having the more constrained form were quite
> >tricky, so we ended up saying just 'Resource'...
> 
> I also dimly recall this decision being made, and that at the time 
> the reasons seemed good to me. I don't think it was because the 
> narrower interpretation presented any particular mathematical 
> difficulties. It may have been the observation that reification 
> should be able to describe 'illegal' RDF, in which a non-property 
> URIreference is used in a predicate position in a triple. At any 
> rate, the mere possibility of such an error occurring means that one 
> should not be able to conclude, merely from the fact of a URI being 
> used in some RDF in this position, that it really does, in fact, 
> denote a genuine property (which would be the effect of having the 
> range be rdf:Property)

Aha, that makes sense. I don't recall ever having realised this! Thanks :)

> It might be worth remarking that to have rdfs:Resouce as a domain or 
> range is never an error, since in RDFS domains and ranges can be 
> conjoined. It is more like a kind of resignation: one is saying that 
> the subject or object of the property may be anything whatsoever, 
> unless of course further information is supplied which restricts them 
> in some other way or for some other reason. One can see this by 
> looking at the RDFS inference rules 
> (http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#RDFSRules), where 
> rdfs3 allows you to conclude in this case that the type of the object 
> of any assertion of rdf:Property must be rdfs:Resource; but one knew 
> that already, from rdfs4b. So this 'vacuous' range only provides some 
> redundant information.

Yep. I wish we'd given a name to the class of non-Literal resources.

(Maybe we'll make a 'handy utilities' namespace eventually...?)

cheers,

Dan
Received on Monday, 29 November 2004 20:25:20 UTC

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