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Subject: discussion of the Creative Commons Metadata work

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  • From: Norman Gray <norman AT astro.gla.ac.uk>
  • To: cc-metadata AT lists.ibiblio.org
  • Subject: rdf:about and PURLs
  • Date: Sat, 23 Jul 2005 00:02:03 +0100


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


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






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