From: Peter F. Patel-Schneider (firstname.lastname@example.org)
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. peter 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 difficulties. 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 rules? 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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