Thank you for this approach, Wolfgang. That sounds great. :)
I just have some further question about your solution.
#1
I'm thinking about an approach without the need modifying things outside
the drl file. Is something like that doable?
Because I have to create the watcher class? (I don't expect it to be,
but why not ask. ;))
#2
(What and count are somewhat redundant, but this avoids clumsy patterns.)
Am I right that what and count have to be defined as global variables
and initialized using setGlobal() (from a part of the java application)?
#3
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
) ) )
I'm sorry, could you explain to me the part of $eventB in sentences,
please? I've got confused by the comments... :(
Thank you very much! :)
Tina
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 <tviessm...@stud.hs-bremen.de
<mailto:tviessm...@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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