[rules-users] Drools + EMF + CDO

[Wolfgang Laun]

On 2 August 2010 12:14, Wolfgang Laun <wolfgang.laun at gmail.com> wrote:

> Several remarks:
> (1) Make sure that a parent is asserted after all of its children.
> Otherwise initial evaluation will not comprise the entire children's list.
>

What I meant is: after all children have been adder to the parent's list,
and *then* insert the parent.


> (2) After changing a child's state, update the parent.
> (3) The rule as you have it now is somewhat circumstantial. A simpler
> approach would be
>
> rule NoUpChild
> when
>     $p : Device(  $children : eContents, eContents.size > 0 )
>     not( Device( state == "UP" ) from $children )
> then
>     System.out.println( $p.getId() + ": no child up" );
> end
>
> (4) If you have a "parent" field, this could even be written:
>
> rule NoUpChild
> when
>     $p : Device(   children.size > 0 )
>     not( Device( parent == $p, state == "UP" ) )
> then
>     System.out.println( $p.getId() + ": no child up" );
> end
>
>
And this would make the additional update according to (2) unnecessary.


> -W
>
>
>
> 2010/8/2 Georg Maier <Georg.Maier at cjt.de>
>
>>  Hi,
>>
>>
>>
>> I’m trying to figure out an issue for three days now and I’m getting kind
>> of desperate, so I hope someone can help.
>>
>> I’m using Drools in combination with an EMF model which is modeling a
>> computer network. On init, I read the whole structure of the model and
>> insert all elements into the working memory. Some of the entities share the
>> super class “Device” which has an attribute “state”.
>>
>>
>>
>> Now I’m having the following rule to change an attribute of one of the
>> model entities:
>>
>>
>>
>> *rule* "Set received status to model"
>>
>>       *when*
>>
>>             $event : SomeEvent (
>>
>>                   $hostname : hostname,
>>
>>                   $hoststate : hoststate,
>>
>>                   $timestamp : timestamp
>>
>>             )
>>
>>
>>
>>             $device : Device (
>>
>>                   name == $hostname
>>
>>             )
>>
>>
>>
>>       *then*
>>
>>             *modify*($device) {
>>
>>                   setState($hoststate);
>>
>>             }
>>
>>             db.commit(*false*);
>>
>>
>>
>>             *retract*($event);
>>
>>             System.err.println("Set status of " + $device + " to " +
>> $hoststate);
>>
>> *end*
>>
>>
>>
>> … which works perfectly fine. Anyway, what I want to do in this test case
>> is to *react whenever all child devices of a mutual parent device* (e.g.
>> hosts on one switch) are no longer reachable. I thought of a rule like the
>> following:
>>
>>
>>
>> *rule* "Parent Children Test"
>>
>>       *when*
>>
>>             $parent : Device (
>>
>>                   $children : eContents,
>>
>>                   eContents.size > 0
>>
>>             )
>>
>>
>>
>>             *forall* (
>>
>>                   $child : Device (
>>
>>                         state == "DOWN"
>>
>>                   ) *from* $children
>>
>>             )
>>
>>
>>
>>       *then*
>>
>>             …
>>
>> *end*
>>
>> * *
>>
>> … which by the way worked perfectly fine as long as I was not using
>> objects from a model. My first idea was that for some strange reason the
>> object might get copied so that I actually would have two different
>> references after modifying it, but this is not the case. When I initialize
>> the rule base with the circumstances that the second rule would fire, it
>> really does. It just seems as it would not being evaluated after changing
>> the attribute, but this is not the case either! So all I can think of is
>> some strange caching, maybe in combination with the *forall *statement?
>> Maybe someone has some experience when using Drools with EMF + CDO and
>> experienced as similar issue?
>>
>> Any help would be very very very much appreciated!
>>
>> Thanks in advance
>>
>>
>>
>> Georg
>>
>> _______________________________________________
>> rules-users mailing list
>> rules-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>>
>>
>
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