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From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Tue, 12 Sep 2006 11:33:59 +0100
Message-Id: <340B375B-47BC-442A-AF1F-AEBEED980CB2@cs.man.ac.uk>
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>

I'm raising this mostly on behalf of Jorge Pérez, Axel Polleres, and  
myself, though we all have slightly different perspectives. I


"""One may test that a graph pattern is not expressed by specifying  
an optional graph pattern that introduces a variable and testing to  
see that the variable is not bound. This is called Negation as  
Failure in logic programming."""

The main concern is that if we are going to allow NAF (which we  
currently do), then we should allow for it in a more convenient form,  
e.g., a not or \+ operator. I think if we stick with it in this  
limited form, then we should call it out better as it's a pretty  
fundamental (though very useful) shift in SemWeb philosophy at the  
W3C. We might also want to coordinate with the RIF about it as they  
will almost certainly be defining NAFy operators.

The other option is to kill bound and unbound. Jorge claims that  
bound is never useful, i.e., never alters results; I haven't worked  
that out myself yet. Jorge also claims "some of the hard results of  
complexity are heaviily involved with the use of !bound", which isn't  
*too* surprising as  nonmon typically raises complexity.

I welcome pointers to past discussions.

Received on Tuesday, 12 September 2006 10:34:00 UTC

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