- From: Pat Hayes <phayes@ihmc.us>
- Date: Tue, 12 Sep 2006 17:19:24 -0500
- To: Bijan Parsia <bparsia@cs.man.ac.uk>
- Cc: 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 > >http://www.w3.org/2001/sw/DataAccess/rq23/rq24.html#func-bound > >"""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) Well, wait a minute. I don't think that we do. And I would prefer that the spec not mention NAF this explicitly. Just checking that something is not present in the KB does not, in itself, constitute NAF reasoning. What makes it NAF is to infer from its absence that it is false, and *that* isn't sanctioned either by the RDF or SPARQL semantics, although to be fair its also not explicitly ruled out by them either. It seems to me that being able to detect non-binding - which I agree is too useful for us not to provide it - is what might be called NAF-neutral: it allows someone to implement NAF if they want to, but it does not of itself sanction it semantically. Which, I suggest, is exactly the stance we should adopt, since RDF is also neutral on the matter. It is possible to have an RDF semantic extension which would make NAF valid, as well as those like OWL that do not. >, 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. I don't think that what we have now amounts to a shift of policy. I agree we should state it differently, and more carefully, than we currently do, however. Pat >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. > >Cheers, >Bijan. -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Tuesday, 12 September 2006 22:19:42 UTC