rdf:about and PURLs

Norman Gray norman at astro.gla.ac.uk
Fri Jul 22 19:02:03 EDT 2005


Greetings,

This is partly an RDF question, but it's pretty immediately pertinent  
in the context of writing CC metadata, hence the posting here.

Say I want to attach some licence declarations to a web document  
referred to by a PURL -- what URL should I put in the rdf:about slot?

PURLs work by having a PURL resolver issue an HTTP redirect which  
maps the PURL to the URL where the object is actually stored.  Thus  
the object has _two_ URIs which refer to it, with one being the URL  
which actually retrieves it, and the other one being the one which  
has the extrasyntactic/social/whatever committment to persistence.   
It is this latter one which is the object's `real' name, and thus the  
one which I, as its maintainer, wish to make statements about.   
Naturally, therefore, it seems that I ought to make my RDF CC  
assertions with reference to the PURL.

However the second, actually dereferencable, URL is a legitimate  
alternative to the PURL, in both the practical sense that it works,  
and the social sense that I can't legislate against that working one  
being the one that some dunce passes around.  If someone retrieves my  
HTML document (or PDF or MP3) using this second URL, they are going  
to find somewhere inside it an RDF block making a number of  
assertions about a completely separate PURL, which has no connection  
with the document they're retrieved other than those connections  
supplied by common sense, native wit, and statements of the bleedin'  
obvious (a most debased currency on the semantic web).

The problem is fairly obvious expressed in terms of PURLs.  But it  
also applies to DOIs, for example: statements about doi:10.1000/202  
and <http://dx.doi.org/10.1000/202> are common-sensibly related; but  
neither is in the least obviously related to <http://www.doi.org/ 
overview/041217DOIOverview.pdf>.

There's no RDFS isEquivalentTo property which I could use to assert  
that statements about a PURL should also be taken to refer to that  
PURL's mappings.  There is in OWL, but dragging in the whole OWL  
mechanism just to solve this problem seems the teensiest bit over the  
top.

I'm firmly braced to be told that this is one of the most tediously  
rehashed problems in this area (though inasmuch as it is a practical  
problem of copyright assertions, it is not the same as the `what is  
the referent of a homepage' hardy perennial).  In which case, can all  
of the above be turned into a request for a more obvious FAQ answer  
on the creativecommons pages?

So which URl do I use?

All the best,

Norman


-- 
----------------------------------------------------------------------
Norman Gray  :  Physics & Astronomy, Glasgow University, UK
http://www.astro.gla.ac.uk/users/norman/  :  www.starlink.ac.uk





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