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Re: [RIF] A Modest Proposal: Work Out Some Concrete Examples; Example-1: CHANGE-BABY-IF-WET rule

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Thu, 26 Jan 2006 22:13:39 -0500
To: "Ginsberg, Allen" <AGINSBERG@imc.mitre.org>
Cc: public-rif-wg@w3.org
Message-Id: <20060127031339.2144A207378@kiferdesk.lmc.cs.sunysb.edu>

You are trying to use first-order logic to analyze what this logic is
ill-suited to do. It is a production rule whose semantics is best and
described in Transaction Logic
For instance, in
FLORA-2, which supports much of Transaction Logic, this Jess rule would
look like this:

changeBabyIfWet(?Baby) :-

change(?Baby) can also be defined via a rule as deleting the old diaper and
inserting a new one where appropriate. The exact definition depends on how
exactly you represent diapers and the fact that a particular diaper is on a
particular baby.

In Transaction Logic, the above changeBabyIfWet(?Baby) would be a
state-changing action. It is defined as a sequence of queries and other
actions. In our case, it is defined as a query (wet(?Baby)) followed by an
action (changeBaby(?Baby)), which changes the underlying state by replacing
the old diaper with a new one, and then deleting the fact that the
specified baby is wet. 


"Ginsberg, Allen" <AGINSBERG@imc.mitre.org> writes:
> Dear RIF-WGers,
> It seems to me that one way of clarifying what the RIF is and what it
> can or should enable is to work on some concrete examples.
> So here is a contribution to that effort:
> Consider the following rule definition (taken from the book "Jess in
> Action" by Ernest Friedman-Hill, p. 98)
> (For those not familiar with this syntax I have provided comments.)
> (defrule change-baby-if-wet 
> 	 // bind the working memory element that satisfied the pattern to the variable ?wet
> 	?wet <- (baby-is-wet) 
> 	=>
> 	(change-baby)
> 	// remove the element bound to the variable ?wet from the working memory
> 	(retract ?wet)  
> )
> Here are some questions: 
> 1) From a theoretical point of view, is there a single optimal or
> correct analysis of the "semantics" of this rule?
>    Or is it possible that more than one reasonable analysis can be
> given?  If so, must these analyses be equivalent?
>    To flesh this out a bit, here are two possible analyses
> 	(A) the meaning of this rule can be represented in classical
> propositional logic as follows:
> 		(P & Q) -> (R & S)
> 	where 
> 		P = "The variable ?wet is bound to an element in
> working memory"
> 		Q = "The fact [baby-is-wet] is in working memory"
> 		R = "The fact [baby-is-changed] is in working memory"
> 		S = "The element bound to variable ?wet is not in the
> working memory"
>      OR  (B) using first-order logic we might try something like
> 	  (ForAll x)(Forall y) (Forall t) 
> 		[ InWM(y,t) & y = fact("baby-is-wet") & Bound(x, y) ->
> (Exists z) (z = fact("change-baby")) & InWM(z,t+1) & ~InWM(y,t+1) ]
> 	Where 
> 		InWM(x,t) = "x is in Working Memory at time t"
> 		fact(<string>) is a function that returns the fact
> associated with <string>
>             Bound(x,y) = "x is bound to y"
> To me, analysis (B) captures more of what is going on then analysis
> (A). However, both analysis represent the meaning of the original rule
> in terms of a formal language that has well-defined semantics itself.
> Neither analysis is complete because they do not explicate the
> predicates or terms involved in their representations of the rule
> meaning, but that could be done.  In particular, there is a discrete
> time-model involved regarding Working Memory that needs to fleshed out.
> 2) Assuming an analysis like (B) is more in line with our understanding
> and expectation concerning the RIF, how should it be done in the RIF?  
>    Rather than answering that question I would state some criteria on
> any proposed answer (relative to this concrete example for now):
> 	1) It should be clear that the RIF representation of the
> change-baby-if-wet-rule can be generated by a general algorithm
> 	2) It should be clear that the resulting representation can be
> used to generate an equivalent change-baby-if-wet rule in systems that
> belong
> 		to the same family as CLIPS/JESS, for example, JRULES. 
> 	3) For systems in a different family (having a different
> meta-model) such as a prolog-based system, the RIF should make it
> possible to transform
>          the original RIF representation of the meaning of the
> change-baby-if-wet rule into a RIF-representation of the meaning of
> that rule in the for
>           systems in the other family.
> NEXT STEPS for example-1:  
>     1) Find equivalent rules for change-baby-if-wet rule in other
> systems in the same family
>     2) Find equivalent rules for change-baby-if-wet rule in other
> systems in different families
>     3) for each of the families on step (2), figure out reasonable
> possible representations of the meaning of the change-baby-if-wet rule
> in terms
>          of a language or model that has well-known semantics.
> _______________________________________________________________
> Dr. Allen Ginsberg        The MITRE Corporation, Information Semantics 
> aginsberg@mitre.org       Center for Innovative Computing & Informatics
> Voice: 703-983-1604       7515 Colshire Drive, M/S H305 
> Fax:   703-983-1379       McLean, VA 22102-7508, USA 
Received on Friday, 27 January 2006 03:13:43 UTC

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