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