I would have all of the object be of the same type or implement the same interface (A), then set some calculated facts in a rule that I would use in a subsequent rule to get the final calculation. This first rule fires for every instance of the type or interface If A.weight > 0 Then Set fact calculated_weight = calculated_weight + A.weight Set fact calculated_certaintity = calculated_certaintity + A.certaintity * A.weight If True Then Set fact final_answer = calculated_certaintity / calculated_weight. Something like that. Hope it helps Barry From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of thomas kukofka Sent: Friday, August 29, 2008 10:08 AM To: Rules Users List Subject: [rules-users] rule algorithm Hello, I search a rule implementation for the following calculation: I have n Objects of differents types (A, B, C, ...) each with a parameter certainty. the overall certainty is calculated as follows: certaintyOverall = (certaintyA * weightA + certaintyB * weightB + ... ) / (weightA + weightB + ...) If it can be assumed that all Objects in the formula always exist it's quite easy: when A (certaintyA: certainty) B (certaintyB: certainty) ... then certaintyOverall = (certaintyA * weightA + certaintyB * weightB + ... ) / (weightA + weightB + ...) But if one ore more objects are missing the formula should be reduced to the certainty and weights of the existing objects. But there are too many combinations of existing/nonexisting objects. How can this be implemented in Drools? Regards Thomas

Or an accumulate function (as long as all you objects implement a commong interface): rule "overall certainty" when $cert : Number() from accumulate( $f : CertaintyFacts( ), overallCertainty( $f ) ) then // do something with $cert end Implement your own formula inside overallCertainty function . []s Edson 2008/8/29 Greg Barton <greg_barton(a)yahoo.com&gt; -- Edson Tirelli JBoss Drools Core Development JBoss, a division of Red Hat @ www.jboss.com