[rules-users] Constaint evaluation

Wed Jun 10 15:55:18 EDT 2009

Ok, so now I understand that the "immutable" is really a concept but not necessarily "enforced". So, the rule conditions get evaluated each time the working memory is updated (and not globals) and rules for which the conditions are true at each evaluation will fire. The execution of the rules will end when there is no more rules for which the conditions are true. Am I correct?

Thanks

-----Original Message-----
From: rules-users-bounces at lists.jboss.org [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Greg Barton
Sent: Wednesday, June 10, 2009 3:49 PM
To: Rules Users List
Subject: RE: [rules-users] Constaint evaluation

The ideas is that objects in working memory are those that meant to be tracked: their changes are made visible to the rules via the insert/update/retract methods.  A global is not in working memory, so it's changes cannot be tracked.  You can change the contents of a global all day long and the rules would never be notified.

It's a similar concept to threads and synchronization.  You can have unsynchronized access to member variables in a class when in a multithreaded environment, but the results are unpredictable.  Likewise, you can use globals in conditions, and change the value of the global as you go, but the results are unpredictable.  

--- On Wed, 6/10/09, Malenfant, Andre <andre.malenfant at cgi.com> wrote:

> From: Malenfant, Andre <andre.malenfant at cgi.com>
> Subject: RE: [rules-users] Constaint evaluation
> To: "Kris Verlaenen" <Kris.Verlaenen at cs.kuleuven.be>
> Cc: "Rules Users List" <rules-users at lists.jboss.org>
> Date: Wednesday, June 10, 2009, 2:20 PM
> Thanks Kris,
> 
> I will try with code constraints.
> 
> But on the globals subject, I read in the documentation
> that one should not use a global in a rule. I have trouble
> understanding why. I don't think drools clones the global
> object (might not be possible anyway). If my rule
> consequences change the state of a global (this usage is
> considered valid as per the documentation as well) then what
> is the harm of using it in a condition? I could understand
> with immutable objects like String but...
> 
> I can change my code to insert that global in the working
> memory but I would like to understand why I should do so...
> And if I do and the state of that object is changed by a
> consequence of my rules, I have to call update? For the same
> reason? I guess I am trying to understand the underlying
> mechanism.
> 
> Thanks
> 
> 
> -----Original Message-----
> From: Kris Verlaenen [mailto:Kris.Verlaenen at cs.kuleuven.be]
> 
> Sent: Wednesday, June 10, 2009 11:38 AM
> To: Rules Users List; Malenfant, Andre
> Cc: Rules Users List
> Subject: Re: [rules-users] Constaint evaluation
> 
> It depends on what type of constraint you are using.
> 
> If you are using a rule constraint, that constraint will be
> evaluated
> just the same as normal rules.  This means that the
> constraints are
> evaluated when data is inserted / updated / removed. 
> Note that, if you
> want to make sure the engine is using up-to-date
> information, you must
> notify the engine (using update) when you change the data
> in the working
> memory.  Also note that globals are considered
> immutable.  You should
> never write rules that depend on the state of a global and
> where the
> global can be changed.
> 
> If you are using code constraints, the constraint is
> evaluated at the
> point the code constraint is reached.
> 
> Kris
> 
> Quoting "Malenfant, Andre" <andre.malenfant at cgi.com>:
> 
> > I have some trouble understanding how conditions and
> constraints are
> > evaluated:
> > 
> > I have a rule flow split node with constraints on a
> global object.
> > The split node always takes the same path like if the
> constraints are
> > evaluated at the beginning of the execution of the
> process and not
> > when the process flow reaches that split node. What I
> would expect is
> > that the split node constraints takes into account the
> state of the
> > global object as modified by previous rules in the
> flow.
> > 
> > Am I right to think that rules conditions and split
> nodes constraints
> > are evaluated only when inserting/updating objects in
> the working
> > memory? The documentation is not really useful (unless
> I haven't
> > found the appropriate one).
> > 
> > Thanks
> > 
> > André
> > 
> > -----Original Message-----
> > From: rules-users-bounces at lists.jboss.org
> > [mailto:rules-users-bounces at lists.jboss.org]
> On Behalf Of Malenfant,
> > Andre
> > Sent: Wednesday, June 10, 2009 11:07 AM
> > To: Kris Verlaenen
> > Cc: Rules Users List
> > Subject: RE: [rules-users] Globals in ruleflow
> > 
> > Thanks for trying this for me...
> > 
> > As it turns out, while I was creating a test sample
> for you I
> > realized
> > that my ruleflow was not loading properly and I forgot
> to check for
> > errors on the builder. Now it works.
> > 
> > Still, the behavior is strange. If my rule doesn't
> load and even
> > though
> > my DRL loaded, my globals were not available. Since
> the DRL declared
> > the
> > same globals it should not have given me that error.
> > 
> > Thanks
> > 
> > -----Original Message-----
> > From: Kris Verlaenen [mailto:Kris.Verlaenen at cs.kuleuven.be]
> 
> > Sent: Tuesday, June 09, 2009 5:51 PM
> > To: Rules Users List; Malenfant, Andre
> > Cc: Rules Users List
> > Subject: Re: [rules-users] Globals in ruleflow
> > 
> > Andre,
> > 
> > There should be no problem in using the same global in
> both your
> > rules
> > and processes.
> > 
> > I have tried a simple example as you described but
> have not been able
> > to
> > reproduce the problem.  Could you send me a
> self-contained example
> > that
> > shows the issue?
> > 
> > Kris
> > 
> > Quoting "Malenfant, Andre" <andre.malenfant at cgi.com>:
> > 
> > > I am experimenting with rule flows and I get the
> following error:
> > > 
> > > Unexpected global [myglobal]
> > > 
> > > When calling setGlobal on the session.
> > > 
> > > This code works without the workflow (globals
> declared in the drl)
> > > but
> > > fails when I include the rule flow. I declared
> the same globals in
> > > the
> > > rule flow in the header section.
> > > 
> > > _______________________________________________
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> > > rules-users at lists.jboss.org
> > > https://lists.jboss.org/mailman/listinfo/rules-users
> > > 
> > 
> > 
> > 
> > 
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> 
> 
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