From: Ian Horrocks (horrocks@cs.man.ac.uk)
Date: 11/05/03
On November 4, Benjamin Grosof writes: > At 05:26 PM 11/4/2003 -0600, pat hayes wrote: > >Suggestion, following Ben's reporting of Tim's observation. The ideas that > >(1) an empty consequent is 'false' and (2) that a consequent is a > >conjunction, are in opposition. The former arises historically from > >thinking of a rule as an implication or a sequent, where a compound > >consequent would be considered a disjunction. I think this is a > >fundamental snag in the current proposal ( sorry I didnt notice it before) > >and suggest that we change the basic rule syntax slightly so that > >consequents are atomic, not conjunctive, but then allow the present case > >as a Lloyd-Topor style syntactic sugar for a conjunction of rules. This > >changes the presentation slightly but makes it natural for an empty > >consequent to be considered a missing atom - false - rather than an empty > >conjunction - true. It also simplifies the semantics, and makes the > >Lloyd-Topor mapping work properly in all cases. > > this is fine by me as a way to define things. 6 of one, half dozen of > another. the main point is to make sure we explicitly define the case of > empty head to mean false, rather than just say something like "the head is > a possibly-empty conjunction of atoms". This is already the case, as you will see from the semantics: "A binding B(I) satisfies a consequent C iff C is not empty and B(I) satisfies every atom in C." Ian > > > >Pat > >-- > >--------------------------------------------------------------------- > >IHMC (850)434 8903 or (650)494 3973 home > >40 South Alcaniz St. (850)202 4416 office > >Pensacola (850)202 4440 fax > >FL 32501 (850)291 0667 cell > >phayes@ihmc.us http://www.ihmc.us/users/phayes > > > > ________________________________________________________________________________________________ > Prof. Benjamin Grosof > Web Technologies for E-Commerce, Business Policies, E-Contracting, Rules, > XML, Agents, Semantic Web Services > MIT Sloan School of Management, Information Technology group > http://ebusiness.mit.edu/bgrosof or http://www.mit.edu/~bgrosof
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