[rules-users] Correlating 2 independent streams of events

[Esteban Aliverti]

Thanks Wolfgang.
I was trying to solve the whole situation with just 1 rule, but not I'm
trying to separate the problem in multiple rules. There are some
bugs/language-limitations/programmer-skills-limitations that are preventing
me to get the expected results though.

Let's say I have a rule identifying my last 3 EventA (ALL my facts are
declared as events):


declare Last3A
    @role(event)
    firstEvent: EventA
    lastEvent: EventA
end

rule 'Detect last 3'
when
   //some magic using sliding windows
then
   //$firstEventA and $lastEventA are the bounds identified in the LHS of
the rule.
   //EventA class doesn't have an explicit timestamp (drools is providing
it) and I'd prefer to leave it that way.
   insert (new Last3A($fistEventA, $lastEventA));
end


Then I have my rule trying to get the occurences of EventB that happen
during a Last3A

rule 'Get EventBs'
when
   $l: Last3A()
   //originally, I've used a collect here since I wanted a single
activation, but I'll use a single event here just to make syntax cleaner.
   EventB(this after $l.firstEvent,this before $l.lastEvent)
then
   ...
end

If I try the latter rule, after I insert the third EventA (I'm calling
fireAllRules() after each insertion) I get the following exception:

*Exception executing consequence for rule "Detect last 3" in com.whatever:
java.lang.ClassCastException: com.whatever.EventA cannot be cast to
java.lang.Number*
*...*
*Caused by: java.lang.ClassCastException: **com.whatever.EventA** cannot be
cast to java.lang.Number
*
*at
org.drools.base.evaluators.AfterEvaluatorDefinition$AfterEvaluator.evaluateCachedLeft(AfterEvaluatorDefinition.java:341)
*

I'm assuming Drools is trying to cast the result of $l.firstEvent into a
number (probably because it is expecting a timestamp) even though the
result is already an Event.

In order to avoid the $l.firstEvent and $l.lastEvent invocations I re-wrote
the rule as follows (is ugly, I know):

rule 'Get EventBs'
when
   $l: Last3A()
   $firstEvent: EventA() from $l.getFirstEvent()
   $lastEvent:  EventA() from $l.getLastEvent()
   EventB(this after $firstEvent,this before $lastEvent)
then
   ...
end

The exception now is:

*Exception executing consequence for rule **"Detect last 3"** in
com.cognitive.nsf.management: java.lang.ClassCastException:
org.drools.common.DefaultFactHandle cannot be cast to
org.drools.common.EventFactHandle*
*
*
What is happening now is that Drools doesn't realize that the object I'm
using for after and before are actually Events.
So it seems that temporal operators can only be used with events coming
from the same rule (and not coming from a 'from' or any other black box).
I'll continue digging on this, but it seems that the only solution will be
to use explicit time stamps and then use them instead of the events in my
marker fact.

Best Regards,






XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Esteban Aliverti
- Blog @ http://ilesteban.wordpress.com


On Mon, Jan 7, 2013 at 12:17 PM, Wolfgang Laun <wolfgang.laun at gmail.com>wrote:

> Use "wrapper" or "marker" facts to identify the last three EventA's
> and a rule to "push" EventA's through these markers. Then, a simple
> rule will give you all EventBs between the extremes of the marker set.
>
> Take care to get the start-up right ;-)
>
> -W
>
> On 07/01/2013, Esteban Aliverti <esteban.aliverti at gmail.com> wrote:
> > Let's say I have two independent streams of different events: EventA and
> > EventB. Which is the best way to get all the occurrences of EventB that
> > happened between the last 3 occurrences of EventA?
> >
> > For example:
> >
> > from:
> > $b1:EventB, $a1:EventA, $b2:EventB, $b3:EventB, $a2:EventA,
> > $b4:EventB, $b5:EventB, $a3:EventA, $b6:EventB
> >
> > I would like to get $b2, $b3, $b4, $b5
> >
> > Best Regards,
> >
> >
> >
> >
> > XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
> >
> > Esteban Aliverti
> > - Blog @ http://ilesteban.wordpress.com
> >
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