% suggestions wrt roadmap for Rules in the Joint Committee
% by Benjamin Grosof 5/6/03

Currently, we have two loosely-coupled efforts:
1. on Rules syntax and expressiveness, starting from RuleML
    and (to a lesser degree so far) Common Logic as primary points of departure
2. on use cases
Both involve analysis of requirements.

My suggestions for today address primarily (1.).
(2.) should definitely continue and be coordinated increasingly
closely with (1.). 

I suggest several phases, to tackle various issues; see below.
I've probably forgotten to include some issues, and quite possibly
some more will arise during our design efforts.  But I think
I've listed at least most of the issues.  


Phase I:  we start with defining:

o Datalog Horn logic programs, with URIrefs for predicate etc. logical
constants, cf. RuleML; and 
coordinate/cross-fertilize this with the specification of 
Datalog Horn FOL in Common Logic.  
(Datalog here means without logical functions of non-zero arity.)

o then Horn without the Datalog restriction

o then extend with various additional features cf. RuleML's existing (V0.8)
or currently-in-discussion designs, again coordinating this with
the specification of Common Logic.


Phase II:  
I've organized these into four groups of issues.
A reasonable sequence would be to tackle them in the following order. 
But one could actually pursue them in nearly any sequence
(there are a few dependencies).   

Group A:

Here are some additional features which apply in the pure-belief
logically-monotonic case, and thus also pertain straightforwardly
to Common Logic as well:

o modules:  i.e., named rule subsets that can be imported.
This is a key Webizing feature.

o object-oriented argument collections:  called "roli" in RuleML V0.8

o Lloyd-Topor And-Or:  permit AND in the head; also permit OR (nestedly
with AND) in the body 

o sorted/typed variables and constants:  where the sort or type is 
a pure predicate/class rather than (directly and more generally/impurely)
a programming language concrete type

o explicit equality predicate


Group B:  

o rest of FOL in Common Logic:
notably quantifiers, classical negation, equivalences.   


Group C:  

Here are some additional features which involve non-monotonicity:

o negation-as-failure (NAF)

o Courteous / prioritized conflict handling

o selective closed-world-assumptions -- 
can often, or perhaps always, be defined as a special case of NAF or Courteous

o strong negation ("classical negation" in the limited sense used in 
extensions of LP)

o full Lloyd-Topor transformation 


Group D:

o Situated / procedural attachments:  NB:  sensing includes an 
important connection to querying and DQL

o Events handling


Phase III:  

An OWL meta-ontology of expressive features above, 
and also of important/frequently-used restrictions, e.g., stratified 
use of NAF, or predicates with arity of at most 2.    










Phase IV: