% notes from JC telecon 6/3/03
% by Benjamin Grosof

Benj reviewed the basic definition of Horn LP

can intro extensions which are reducible to the basic:
- OR in body
- existential in body
- AND in head
- universal in head

Pat:  motivations for the definition and semantics?

Gerd:  natural for executable to have a single intended [partial] model,
similar to databases

Pat:  Herbrand is useful for meta-theoretic and syntactic

Benj:  has simplicity for implementation and also for specification

Pat:  these questions will reemerge

Mike:  e.g., how should it relate to semantics of RDF or OWL, as a target
- Pat:  RDF is basically existential conjunctive logic
- Benj: LP is actually much more established than DL or RDF or OWL
- Mike: try to conform to OWL, head off any incompatibilities

Pat:  differences between LP and OWL/RDF include:  
RDF and OWL all have classical model theories
LP is fundamentally not monotonic and is recursive; it plays a different
game

Gerd:  would not be as pessimistic as you

Benj:  don't get hung up on the terminology of "model":  
the Horn LP conclusion set corresponds to the set of ground atoms
that are entailed in Horn FOL

Pat:  example:  RDF or OWL ontology that talks about colors,
e.g., red, green, blue, that is integrated with PanTone (spelling?) 
which has URI's, and printing and a color-checking engine;
in Horn LP model theory a name refers to itself, so can't
express this well; will wreck things.

Benj:  elaborate please?

Pat:  point is that URI's have genuine denotations in the world

Benj:  that's orthogonal to Herbrand-ness unless you can represent within 
the KR some info relating the denoter to the denotation 

Ian:  why stop at Horn LP rather than Horn FOL?

Benj:  because it's well understood at a research level how to extend it to 
non-monotonicity and procedural attachments, but not to do so by extending FOL
(tho' some procedural attachments can be handled in FOL).
Also Horn LP is a waystation not a final destination -- it gets extended
in two directions:  towards FOL/classical-logic and also towards
fuller LP with nonmon and procedural attachments which is 
commonly used practically and relatively well understood theoretically.

Gerd:  there is a generally used notion of rule systems, that is non-classical,
e.g., has negation-as-failure

Pat:  I'd like to get convinced that logic programs is the right notion that
is widely used [in commercial rule systems] -- feel doubtful on this point

general discussion on this point
- Benj, Gerd, Said observing that 

Said:  policies 

Ian:  lots of these systems mix in programming application development
features, don't they

Said and Benj:  yes

Benj:  but they're closer to declarative LP KR when you project onto
their pure knowledge-based aspect


consensus:  
important topics for future discussion:
- built-ins (next week)
- human-consumption string syntaxes (2 weeks from now)
- explicit equality, names (3 weeks from now)
- semantics of procedural attachments, how to relate that to classical logic