From: Chris Welty <cawelty@gmail.com>

Date: Mon, 04 Feb 2008 23:42:00 -0500

Message-ID: <47A7E918.1080200@gmail.com>

To: Jos de Bruijn <debruijn@inf.unibz.it>

CC: Michael Kifer <kifer@cs.sunysb.edu>, RIF WG <public-rif-wg@w3.org>

Date: Mon, 04 Feb 2008 23:42:00 -0500

Message-ID: <47A7E918.1080200@gmail.com>

To: Jos de Bruijn <debruijn@inf.unibz.it>

CC: Michael Kifer <kifer@cs.sunysb.edu>, RIF WG <public-rif-wg@w3.org>

</chair> Hold on a second. I have to think about the universal quantification bit some more but: Jos de Bruijn wrote: > Michael Kifer wrote: >> >> Say, "a" is true, "b" false, and "c" is undefined. What's the values of >> >> Itruth (a \/ c) = ? >> Itruth (b /\ c) = ? >> >> If it's true/false, then this is exactly the same as adding the undefined >> truth value and a 3-valued logic. We discussed this before. "Undefined" is not a truth value. The point of undefined is that the model theory doesn't tell you what the truth value is in this case. It is NOT defined - that is supposed to mean we don't care. Specifying that undefined is a kind of truth value actually defines it. >> If it is undefined, then this is unacceptable, because it would mean that >> the following ruleset would have no models: >> >> q :- (p, a) \/ (r, c). >> p. So this would have a model. c is undefined so (r,c) is either true or false, it doesn't matter, the BLD spec doesn't tell you which it is. Whichever it is, q is in the model. The point was supposed to be that we leave it up to implementors to deal with errors. BLD doesn't specify the truth value of statements with errors. That's why the mapping is partial. -Chris <chair> -- Dr. Christopher A. Welty IBM Watson Research Center +1.914.784.7055 19 Skyline Dr. cawelty@gmail.com Hawthorne, NY 10532 http://www.research.ibm.com/people/w/weltyReceived on Tuesday, 5 February 2008 04:42:20 UTC

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