[rules-users] Absence Pattern question

[Wolfgang Laun]

Try a rule with a timer:

rule AnoB
timer( int: 3m )
when
    $a: A( status == "waiting for B" )
    not B( this after $a )
then
    modify( $a ){ setStatus( "no B within 3m after me" ) }
end

Untested.
-W


On 5 July 2011 13:00, wendy <w.mungovan at yahoo.com> wrote:

> Hi,
>  I'm having trouble writing an absence pattern.  What I'm trying to do is
> detect when there is an A followed by no Bs for 3+minutes.  I don't care if
> there is more than one A.  What I'm running into is that when I try to use
> 'over window:time' the time within drools is the end time of the window.
>  So
> this means I need to write the no Bs for 3+ min first:
>
> not( $b: B() over window:time(3m))
>
> then try to find the A before it:
>
> $now: Long() from RuleUtilityFunctions.getSessionClockTime()
> $a: A( this before [3m] $now)
>
> then I should have to check to make sure that I don't have any Bs between
> $a's time and the start of the no B window:
>
> not( B( time >= $a.time,
>           time <= $now))
>
> This is not working.  I think that it has something to do with my function
> to get the session clock time (RuleUtilityFunctions.getSessionClockTime())
> and how things get evaluated within the Rete engine.  Because it does not
> seem like $now is getting re-evaluated on future calls that pass the $b
> condition.  If I replace $now with the call to getSessionClockTime()
> everything just seems to get weird.
>
> I've tried to write the rule forward too.  Look for A followed by no B but
> that does not seem to work because A is matched at the current time and the
> rule triggers because there is no B because the future B data has not be
> inserted into working memory yet.
>
> What is the right way to write this rule?   Is there a way to get the start
> and end time of the time window that met the over window:time() condition?
>
> Thank you,
> Wendy
>
>
> --
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