[rules-users] Flow and Rules Together - Best practice question

[Pete Carapetyan]

Nice post, Gerret. Cean logic, nicely presented. Separation of concerns vs
tangled web of dependencies..... woooohooo!

On Thu, Feb 18, 2010 at 3:05 AM, Gerret Hansper <gerret.public at gmx.de>wrote:

> Hi Mike,
>
> I have been working with Drools for only a few months now and am still
> rather
> new to it, but we've have made the same experience, switching from rules
> only to
> rules with flow, and I'm certain it's the right way to go.
>
> The performance implications you mention depend mainly on the way the rules
> are
> set up, I guess.
> That is, if you have expensive RHS expressions like eval() you might indeed
> profit from keeping your glucose-level condition at the beginning of the
> rules
> which would prevent those expressions from being reevaluted, as far as I
> understand.
> If you don't I can hardly imagine that activating the rules makes up a
> noticeable fraction of the overall time of your process.
>
> We here have a scenario where some rules may be activated only if the user
> starting the session has got corresponding privileges.
> Since determining the priviliges is not always trivial we definitely wanted
> to
> have that logic in one place. The first thing to do was to use inference
> (http://docs.codehaus.org/display/LOGICABYSS/Policy+Encapsulation) but
> still
> already with a few dozen rules and including other constraints the rule
> RHsides
> became rather cluttered. Moreover it was getting increasingly complex to
> control the order in which the rules fired, maintanance being another
> issue.
>
> Using a rule flow we have achieved really good separation of concerns: A
> rule's
> RHS mostly contains exactly those conditions that apply to its intent, none
> of
> the cross-concerns or technicalities. (Hey, what about an AspectDrools
> implementation? ;-) )
> I am confident that OO lessons apply here, too: If you have a clean design
> and
> performance problems start to show up you are much more likely to solve
> them
> than if you have a tangled web of dependencies.
>
> Greetings,
>         Gerret
>
>
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