[rules-users] Another solution for: Detecting more than 3 occurrences within 1 hour

[Wolfgang Laun]

Basic idea: associate a Watcher with each event.

class Watcher {
   Value what;
   int count = 1;
   Set<Value> valueSet = new HashSet<Value>();
   Watcher( Value first ){
      valueSet.add( what = first );
   }
   //...
}

And now the rules:

rule attachWatcher
when
  $event : Value( eval(parameterValueExceededLimit($eventA.getAlarms())) )
  not( Watcher( what == $event ) )
then
  insert( new Watcher( $event ) );
end

rule addEvent
when
 $watcher : Watcher( $eventA : what, $set : valueSet )
 $eventB : Value( this after[0ms,1h] $eventA  &&
  //                                   this != $eventA  &&      ### set
includes Watcher.what

 eval(valueExceededLimit($eventB.getAlarms()) && ! $set.contains( this ) ) )
then
  modify( $watcher ){
      setValueList( $watcher.getValueSet().add( $eventB ),
      setCount( $watcher.getCount() + 1 )
  }
end

rule testLimit
when
   $watcher : Watcher( count > Limit )
then
  // raise hell,
  // probably: get rid of all in $watcher.set, and $watcher
end

(What and count are somewhat redundant, but this avoids clumsy patterns.)

Watcher should be declared as Event, with @expires, so they'll disappear
with the (primary) Event each one is watching.

Cheers
-W


2010/8/5 Tina Vießmann <tviessmann at stud.hs-bremen.de>

>  Hi,
>
> I'm working on thinking in Drools rules. Right now I'm trying to solve
> this:
>   The rule shall fire if *a special event occurs more than 3 times within
> 1 hour*.
>
> My *first thought of a solution* was to count the count the detected
> events using a counter. But the counter has to be a global variable, hasn't
> it? And global variables are not to be used to frequently, aren't they?
> And global variables must always be initialized from outside the rules
> file, don't they?
>
> Because of these thoughts I've looked for a *different solution without
> global variables*. I came up with:
>
> function boolean valueExceededLimit(Set<Alarms> alarmSet) {
>    //....
> }
>
> rule "more than 3 occurs within 1 hour"
>
>     when
>         // event #1
>         $eventA : Value(
> eval(parameterValueExceededLimit($eventA.getAlarms())) )
>         // event #2
>         $eventB : Value( this after[0ms,1h] $eventA  &&
>                                     this != $eventA  &&
>
>  eval(valueExceededLimit($eventB.getAlarms())) )
>         // event #3
>         $eventC : Value( this after[0ms,1h] $eventA  &&
>                                     this != $eventA  &&
>                                     this != $eventB  &&
>
>  eval(valueExceededLimit($eventC.getAlarms())) )
>         // event #4  ->  4 > 3
>         $eventD : Value( this after[0ms,1h] $eventA  &&
>                                     this != $eventA  &&
>                                     this != $eventB  &&
>                                     this != $eventC  &&
>
>  eval(valueExceededLimit($eventD.getAlarms())) )
>
>     then
>         // ... do something ...
>
> end
>
>
> More than 3 is kind of a doable task. But I think of this solution as heavy
> in case its needed to detect a larger number of events. I would be thankful
> for other approaches to the problem.
>
>
> Thanks :)
> Tina
>
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>
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