[rules-users] How to track constraint truth [was: Non short circuit ANDing]

[Cotton, Ben]

Nice.  Very straight forward too.



To summarize my understanding:



Given an initial "business rule"  all that has to be done is to implement a Fluent Builder tool that generates the business rule re-write as



1.   an initial root rule (e.g. "car"), that when fired activates a "Collector"



2.   a set of n extended rules (1 for each L-Value predicate participant in the original business rule)



3.   whenever rule i (of the  n extended rules) matches, rule i does Collector booking in its RHS consequence processing. (accounting for predicate participant i)



4.  generate a final set of rules that match on the Collector's account of success/failure and reports on any specific details of that accounting in these final set of rules' callback(s) to the Collector implementation (e.g. your RHS invoke of Collector.missing() to render "price > 1000" as point of failure)



I think I get it, starting to exercise this now.



THANKS WOLFGANG!



P.S.  Wolfgang, do you have any comment wrt to using WM Listener(s) and their event callback processing (in conjunction w/ this pattern) as an effective tactic for helping to account/audit for when rules fail to fire?





-----Original Message-----
From: rules-users-bounces at lists.jboss.org [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Wolfgang Laun
Sent: Saturday, February 02, 2013 5:26 AM
To: Rules Users List
Subject: [rules-users] How to track constraint truth [was: Non short circuit ANDing]



To summarize the discussion of the major part of the cited thread:

   * There are situations when it is of interest to learn which of the several constraints of a rule are true and which block it from firing.

   * It is known that manually writing a set cooperating rules can solve this problem (e.g., Rule Design Pattern "Learning the Reason for

Failure")

   * Some automatism supporting the creation of such a set would help



Considering such a support, one wonders which level of complexity in the primary rule it must be able to handle. The task in itself procures a limitation, e.g., when one pattern must match so that a binding is available which is used in a successive pattern. (More

formally: the dependency graph of bindings restricts the investigation of the truth of LHS sub-terms.) Furthermore, any solution using reverse-engineering from the internal representation of a LHS isn't simple, and the API for accessing a compiled rule isn't "stable".



But I think that simple scenarios can be handled by a simple rule authoring tool. I'll explain this by using an example: a rule investigating offered cars according to a buyer's wishes:

class Car {

   String colour;

   int price;

   int horsepower;

   boolean abs;

}



rule "car"

when

   $car: Car( colour == "red", price < 1000, horsepower >= 150, abs == true ) then ... end



To permit the individual investigation of constraints, this might be rewritten as:



rule "car"

when

   $car: Car()

then end



rule "car colour == \"red\"" extends "car"

when

  Car( this == car, colour == "red" )

then // Gosh, a red one!

end



rule "car price < 1000" extends "car"

when

  Car( this == car, price < 1000 )

then // Hey, it's cheap enough!

end



And so on. - For a fully automatic process, a "Collector" fact has to be maintained for each fact (or Cartesian product of facts) matching the initial rule (i.e., "car"). Into this Collector, positive results from the extending rules are injected, so that, ultimately, it can be examined for full information. Here's a couple of examples of rules doing just that, with the rule id and failure count as positional

properties:



rule "success"

when

    $c: Collector( "car", 0; )

then

    System.out.println( "Found the car I want: " + $c.get( "car" ) ); end



rule "almost"

when

    $c: Collector( "car", 1; )

then

    System.out.println( "Almost the car I want: " + $c.get( "car" ) );

    $c.missing();

end



Given the Car( "red", 1200, 160, true ), the second rule fires and produces:



Almost found the car I want: Car [colour=red, price=1200, horsepower=160, abs=true]

missed: price < 1000 in Car



How to write the original rule is the last point. The actual user interface could be simpler, but here is a basic fluent API:



public String makeRuleText(){

    RuleSet ruleSet = new RuleSet( "com.sample", "car" )

    .add(new BasicPattern( "car", Car.class ) )

    .add( new Constraint( "colour == \"red\"" ) )

    .add( new Constraint( "price < 1000" ) )

    .add( new Constraint( "horsepower >= 150") )

    .add( new Constraint( "abs == true" ) );

    return ruleSet.toString();

}



Cheers

Wolfgang

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