rule proto-proposal

From: Peter F. Patel-Schneider (
Date: 05/29/01

As promised (threatened), I have put together the beginnings of a proprosal
for rules in DAML+OIL.  This is the very initial stages of a proposal, and
has certainly not be analyzed to the extent that it should.


	The Beginnings of a Proposal for Rules in DAML+OIL

WARNING:  This is not a full proposal.  I have not worked out the exact
form of the proposal, nor have I analyzed the proposal for computational

There are many possible views on what a rule can be, ranging from
condition-action rules as in OPS to rules of inference.  I believe that the
latter kind of rule is most appropriate for DAML+OIL, as it maintains the
logical flavour of the formalism.

Thus I propose that rules of the form

	A -> C

where A is the antecedant of the rule, and C is the consequent of the rule,
be added to DAML+OIL.  The semantics of these rules would be

	Whenever (and however) A is true
	C will also be (made) true

Therefore, both A and C have to be things that can be considered to be (or
made) true, and would not have procedural meaning.

So far the proposal is not very specific, only forbidding rules that have
actions.  There are a number of possibilities for the form of A and C.  The
least-powerful version would be have both A and C be DAML+OIL classes.
This version of rules would not be very useful in DAML+OIL, however, as it
can already be expressed in DAML+OIL by stating that A is a subclass of C.

A more-powerful possibility would be to allow A to be a class expression
with tags and allowing these tags to show up in C, which would also be
expanded to be a collection of class expressions---not just a single class.
In this proposal, one could do things like relating the fillers of various
property chains to one another, something like

	PERSON ^ father : x ^ mother : y  -> wife-of(y,x)

There are a number of questions concerning this proposal.

1/ Does it actually add any expressive power?

   I had thought that it would, but now I am less sure of this.

2/ Does it capture an interesting portion of what people want to do with

3/ How hard is it to reason with?

The next step up in expressive power would be to allow the antecedant to be
something like a conjunctive query, by the way.

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