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Re: RDF Keys, or why RDF is lousy at metadata annotations

From: Frank Manola <fmanola@acm.org>
Date: Mon, 15 Mar 2004 12:55:50 -0500
Message-ID: <4055EE26.7050905@acm.org>
To: Bob MacGregor <macgregor@ISI.EDU>
Cc: www-rdf-comments@w3.org

Bob MacGregor wrote:

> Frank,
> It is absolutely essential that keys be composite -- it would
> be unfortunate if there were a long debate on that point.  You
> might as well tell the database folks that they ought to do fine
> with single-column keys.  As a single example, if I'm tracking
> an entity moving in time, the obvious key for each "observation" is
> the URI for the entity combined with the timestamp of the
> observance.  The need for composite keys would seem to imply that OWL's
> inverse functional property is irrelevant.
> As to whether keys belong in OWL, or to the follow-on RDF, I
> would say that a strong argument in favor of putting keys into RDF
> derives from the strong interaction
> between keys and the generation of unique, repeatable URIs.  The URI
> issue seems to me more like an RDF level thing than an OWL thing.
> So, if the RDF folks get serious about annotation and tackle the
> URI problem, then they would want keys to be in place.


Being a "database folk" myself, I'm rather fond of composite keys, and 
wasn't proposing a debate on the subject.  I was merely pointing out 
that the issues of *where* keys should be defined, RDF or OWL, and 
whether they should be composite or not, seemed to be separate issues. 
Still another issue is the relationship between URIs and a key 
mechanism, e.g., whether keys should be considered as some kind of URI 
construction mechanism, as you're describing it above, or whether they 
are considered as a kind of constraint, as they are in OWL (in addition 
to URIs, which are also used in OWL).  Also, while I can see how you 
might find OWL's inverse functional properties "indequate", if what 
you're after is composite keys, I don't see how they can be considered 
"irrelevant".  If we're going to build more powerful ways to identify 
resources into the RDF/OWL stack, we certainly ought to be considering 
related capabilities that are already there (even if we wind up 
reworking them).

Received on Monday, 15 March 2004 12:54:46 UTC

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