Re: [rules-users] 'else' in rule
I fully agree with Jim K. Writing good business rules (and in my opinion good business rules are loosely coupled) is not straightforward and intuitive at the beginning and requires from software engineers to develop a different mindset. Having an ELSE statement could be a deterrent from writing loosely coupled rules which is a good practice IMHO. It reminds me of my early BASIC programming days (in the 80's :) where I would end up with horrible spaghetti code because of my misuse of the infamous GOTO statement. I also vote against the ELSE statement. Spyros -Original Message- From: rules-users-boun...@lists.jboss.org [mailto:rules-users-boun...@lists.jboss.org] On Behalf Of JimK Sent: Tuesday, December 06, 2011 9:08 PM To: rules-users@lists.jboss.org Subject: Re: [rules-users] 'else' in rule 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. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] 'else' in rule
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 mproc...@codehaus.org wrote: On 05/12/2011 18:43, ronalbury wrote: Please consider the possibility of When Then When Then Else It's already specced up in relational data flows which allows a tree-like data flow for your decision: http://community.jboss.org/wiki/RelationalDataFlows I hope that it, or a variation on it, is delivered in 2012. Mark -- 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. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] 'else' in rule
I agree that I jumped in on an effort to define a requirement in terms of a solution ... however, people generally understand else and otherwise, so there is some justification in saying you want something to work like them. I don't care what the underlying mechanism is, but as it stands now we have to write a rule When (condition-A) and then another rule When not (condition-A) ... and I think that makes the rules more difficult to understand and to maintain. Thanks Ron -- View this message in context: http://drools.46999.n3.nabble.com/else-in-rule-tp3264337p3564318.html Sent from the Drools: User forum mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] 'else' in rule
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. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] 'else' in rule
On 06/12/2011 19:08, JimK 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. What is currently in early propsoal stage is a sort of directional data flow concept: http://community.jboss.org/wiki/RelationalDataFlows While there is no 'else' keyword you can control the direction of flow from failure of a tuple to propagate, this allows you create tree like data structures to handle the flow, which can solve else like situations. For me the most interesting and useful construct there will be the case statement, which I find I often need. I'm looking to be able to better handle signal processing type problems, that people might use languages such as erlang for. Mark 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. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] 'else' in rule
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. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] 'else' in rule
On 05/12/2011 18:43, ronalbury wrote: Please consider the possibility of When Then When Then Else It's already specced up in relational data flows which allows a tree-like data flow for your decision: http://community.jboss.org/wiki/RelationalDataFlows I hope that it, or a variation on it, is delivered in 2012. Mark -- 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. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
