% notes from JC telecon 8/12/03
% by Benjamin Grosof

agenda:  
- introduction of new proposal by Peter and Ian
- Rules Lite plans, including work items and volunteering

participants:
Mike Dean
Benjamin Grosof
Peter Patel-Schneider
Harold Boley 
Said Tabet
Ian Horrocks
Pat Hayes
Sandro Hawke
? perhaps one or two others

Peter walked thru the proposal very briefly

Peter:   body and head are each a conjunctive query 

Peter:  adding Horn to DL will result in undecidability 

Benj:  
issue:  explicit inequality (i.e., differentFrom) in head goes beyond Horn;
perhaps reducible if there is a complete theory of equality, but is there

Peter:
another issue:  only-if direction goes beyond Horn

Ian:
actually can express head equality given Horn plus DL expressiveness

Benj:  


(some discussion around desirability/feasibility of decidability)

%%%%

some initial volunteering:

examples and test cases:  Mike, Said, and maybe Deborah

warning label:  Benj and Pat

concrete syntax:  Harold and Said

abstract syntax:  Benj ; 
   would also like later help from someone who worked on OWL abstract syntax 


Benj:  in addition it seems important to soon resolve also the ff.:  
- expressiveness -- esp. what further expressive restrictions or additions


perhaps can defer the ff. additional work items:  

requirements and objectives statement

updated roadmap

semantics -- is simple since is just FOL essentially

running of test cases using various existing tools


agenda for next week:  schedule of these work items


summary of expressiveness issues, earlier discussed, that will need to 
be resolved: [Benj, after the telecon, extracting from telecon discussion] 
- Datalog restriction (probable)
- RDF lists permitted, but probably restricted somewhat:
    . blank nodes -- avoid in head; perhaps also avoid in body 
    . avoid KIF's over-ambitiousness (consensus)
- avoid 0-ary predicates (probable)
- limiting equality as predicate
    . in manner similar to OWL-DL (probable)
    . esp. in head 
- permit conjunction within head in rule syntax, using expressive reducibility 
    . naming of rules might be a complication 
- naming of rules (perhaps defer beyond Rules Lite)
- how tight is layering semantically on top of RDF or OWL 
- be able to handle distributed facts:  import'ing, module union'ing
  . Benj:  propose to defer this a bit, beyond the basic proposal


Benj:  
propose to keep it really simple:
- Datalog, no head b-nodes, no 0-ary predicates, no head equality, 
conjunction within head, do permit rule names, do permit simple RDF lists
- but people should develop test cases if they're worried/irked by these
restrictions

Harold:  Datalog can be problematic for lists unless have b-nodes

Mike:  
would like to do b-nodes; will develop some test cases;
painful not to permit this

Sandro and Benj:  
but that's head existential, and thus not Horn; and permitting just in body
would probably be confusing to users

Pat:  
can get quite a bit of expressive power probably if do include

Benj:
how about we permit head conjunction 

Benj:
is there a way to impose some restrictions on head b-nodes 
that enables reducibility 

Mike:
maybe the real issue is gensym capability, but can't create new names
based on variables if are restricted to be Datalog

Benj A to Pat Q:  the reason to stick to Horn as well-studied expressive class
is that it has available:  
proof theory, completeness, algorithms, implementations 
that are tighter than full FOL 

Benj:  suggest the way to resolve this b-node issue is with some use cases
- Mike; Sandro will help review



agenda for next week: 
- IJCAI report from Ian
- more on Peter and Ian's proposal 
- schedule of our work items
- use cases on b-nodes