Please consider the possibility of When Then When Then Else -- View this message in context: http://drools.46999.n3.nabble.com/else-in-rule-tp3264337p3562187.html Sent from the Drools: User forum mailing list archive at Nabble.com.

The request for "else" is not as simple as it may seem. (Has the fundamental difference between a rule and an if statement impregnated itself?) Given rules when Car(color=Color.RED) then when Car(color=Color.BLUE) then and assuming that we have an "else" linked to these rules, how should this "else" rule fire? (a) Fire once, when there are no RED or BLUE Car facts ano no other Car facts at all. (b) Fire once, when there are no RED or BLUE cars but when there is at least one Car fact, with any other color. (c) When there are no RED or BLUE cars, but fire once for each Car that has any other color. (d) Irrespective of the presence or absence of RED and BLUE Car facts, once for each Car that has any other rule. I am, of course, assuming that rules do not fire mutually exclusive; hence an "else" could fire even when one of its associated "when" rules should fire. There is, of course, a thing called "decision tree", and it's legitimate to expect that a "decision making system" should provide this technique (just like "decision tables"). But I think it should not be tacked onto rules (and you may not even need a Rete engine for that) - the user confusion is bound to reach new levels. -W On 06/12/2011, Mark Proctor <mproctor(a)codehaus.org&gt; wrote:

My $.02 I'm early in my use of Drools and Rules and struggled at first with the lack of ELSE. At first I would frequently feel "an ELSE would be prefect here". After awhile I believe that NOT having Else is a good thing. As I get better with writing rules I find that most of the times when I think I need an Else it usually means I should take a closer look at the rule. If I have a true Else situation for me I put the two rules one right after another. In these situations I think it is better to have to write the "ELSE" rule as effectively a NOT of the WHEN rule then having an ELSE fall through. Isn't that much extra coding and usually gives me pause to give it one more evaluation to see if this is a true ELSE or a new rule with similar criteria from the When. Many times the ELSE covers too many possibilities that should be explicitly checked and for me at least tells me I might not have fully broken the requirements down. As another posting indicates the complexity of implementing it I also wonder about the performance hit the logic to allow for an ELSE would add. With my current understanding of business rules and drools I would vote against an ELSE. Jim K. -- View this message in context: http://drools.46999.n3.nabble.com/else-in-rule-tp3264337p3565278.html Sent from the Drools: User forum mailing list archive at Nabble.com.