Regis,

   It is well known that from a performance perspective, rules engines work more efficiently with flat models than with deeply nested models. That is because rules engines usually implement relational-like algorithms (you can make an analogy to relational database technology).
   It does not mean that you can't use pure OO models in Drools. In fact, drools is one of the engines that better handles OO models (if it is not the best). The example I gave you using "from" instead of the nested accessors should work for your case just fine.

   Now, the immutability of the predicates is a different matter. To keep working memory consistency, drools 4 makes use of shadow facts, that are lazy cache objects implemented as transparent proxies for your facts. Of course, it would not be feasible to cache everything in an object graph, and so, drools caches only the root objects you assert as facts into the working memory. When you use nested accessors, you are obviously accessing non-cached data and for that reason they must be immutable or you will have problems.
   Drools 5 is making the use of shadow proxies not required by implementing a different strategy of constraint evaluation. But that is only in trunk, not in 4.0.x branch.

   []s
   Edson


2008/4/15 Piccand, Regis <rpiccand@verisign.com>:
Hi Edson,
 
Thanks for your help. I restructured my biz objects to avoid nested structures, which makes it work now (I have new objects to hold allocatedHour per subject).
 
However, I have the feeling that this constraint has a certain impact on o-o design (more flat objects vs composite object). The documentation says that nested values should be considered immutable, unless using the modify block (as you suggested) and retract/re-assert the objects in the workingMemory ; it also has a much greater performance cost.
 
Am I getting it right when saying that the object design should really be like 'many flat-type objects avoiding composite approach' to have Drools perform well or is it more sensible to have a proper o-o design and tweak Drools (using modify block, disabling cache, etc.)
 
Thanks in advance for sharing your experience
 
Regis
 
 
 

when

$lesson : Lesson(allocated ==

false
, session.type == Session.DISTINCT)

$subjectAllocation : SubjectAllocation( subject == $lesson.subject, $allocatedDays : allocatedDays )

$availableHour : Hour(allocated ==

false, day not memberOf $allocatedDays)

then

$lesson.setHour($availableHour ) ;

$lesson.setAllocated(

true ) ;

update($lesson) ;

$availableHour.setSubject($lesson.getSubject() ) ;

$availableHour.setAllocated(

true ) ;

update
($availableHour) ;

$subjectAllocation.addAllocation($availableHour ) ;

update($subjectAllocation) ;
 

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Edson Tirelli
Sent: Monday, April 14, 2008 4:55 PM
To: Rules Users List
Subject: Re: [rules-users] newbie: update and shallowCache


   Regis,

   You are probably having problems with mutable predicates, when using "subject.allocatedDays". As a first step to understand your problem, I strongly encourage you to make constraints flat, i.e., avoid using nested accessors. After you get used to what can and what can't be done, you can go back to use nested accessors.
   Also, I suggest you use modify() block instead of update():

rule

"allocate"

when

$lesson : Lesson(allocated == false, session.type == Session.DISTINCT )

$subject : Subject( $allocatedDays : allocatedDays ) from $lesson.subject

$availableHour : Hour(allocated == false, day not memberOf $allocatedDays)

then

modify( $lesson) {

    setHour($availableHour ),

    setAllocated(true)

}

modify( $availableHour )

    setSubject($lesson.getSubject()),

    setAllocated(true )

}

end
    Hope it helps.

    []s
    Edson
 
2008/4/14 Piccand, Regis <rpiccand@verisign.com>:
Hi all,
 
I am evaluating Drools and am stuck with a simple rule that selects elements which do not correspond to the condition... Since I am updating objects in the RHD, I guess it has to do with my wrong understanding (and the cache...?)
 
 
I am trying to allocate lessons to periods (hour). My object model can be summarize is as follows :
 
Lesson
    boolean : allocated    // true if the lesson has been allocated to an hour
    int : session             // a session is a bunch of lessons
    Subject : subject    // an allocated lesson is assigned a subject
 
Subject
    Set<Day> : allocatedDays // days in which this subject is taught - checked before allocation, as a subject can only be taught once a day
 
Hour
    boolean : allocated // true is this hour has been allocated with a lesson
    Day : day // the day this hour belongs to - required to check with subject.allocatedDays
 
 
I put in the workingMemory a bunch of Lesson objects, which have been set with Subject and Session id. I also put a bunch of Hour object, set with a Day.
 
 
My rule is as follows:
 

rule

"allocate"

when

$lesson : Lesson(allocated == false, session.type == Session.DISTINCT, $allocatedDays : subject.allocatedDays)

$availableHour : Hour(allocated == false, day not memberOf $allocatedDays)

then

$lesson.setHour($availableHour ) ;

$lesson.setAllocated(true) ;

update($lesson);

$availableHour.setSubject($lesson.getSubject()) ;

$availableHour.setAllocated(true );

update($availableHour);

end

When I set a debug on the first line of the THEN section, I can see that sometimes $availableHour.allocated == true ... sometimes $lesson.allocated == true (although it's an implicit And statement ...)

Therefore, I can see that the update() works, but it seems that the rule does not use the updated object (due to shallow copy ??)

Any help more than welcome

Regis

 


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--
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
JBoss, a division of Red Hat @ www.jboss.com

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--
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
JBoss, a division of Red Hat @ www.jboss.com