- From: Chris Welty <cawelty@gmail.com>
- Date: Tue, 24 Jul 2007 12:11:35 -0700
- To: Michael Kifer <kifer@cs.sunysb.edu>
- CC: "Boley, Harold" <Harold.Boley@nrc-cnrc.gc.ca>, "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Michael Kifer wrote: >>>> * It seems to me a cleaner syntax is to remove existentials from >>>> conditions and unify all quantifiers outside the rule (as with >>>> universal now), and add a restriction in horn that existentially >>>> quantified vars cannot appear in the conclusion. >>> The RIF Basic Condition Language is meant to be reusable also >>> (in PR and) outside the context of any rule, stand-alone (e.g. >>> for queries and integrity checking), where existentials cannot >>> be rewritten as universals in the Example 3b.->3a. manner. >> Oh, you misunderstood - I did not mean eliminate existentials from the >> syntax entirely, I meant move them outside conditions into some sort >> of wrapper or context (like, rules). This would make, at least, the >> rule syntax cleaner. > > Unless I misunderstood you, what you are proposing is not sound in FOL: > > Exists X foo <- bar(X) > > is not the same as > > foo <- Exists X bar(X). As you know full well this kind of mapping is easily fixed by rewriting the variable names. -Chris -- 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/welty
Received on Tuesday, 24 July 2007 19:11:46 UTC