[rules-users] How to retract events that don't match any rules (without @expires())

[Wolfgang Laun]

If a fact is to be matched right after insertion the solution is
simple: add a rule with low salience matching and retracting the fact.

If you expect/hope that it matches later and you have a time limit,
@expires is the answer.

The interesting case is when you don't have the time limit and still
hope for a match. If you have a convincing use case for that, I might
be enticed to develop a solution for that ;-)

-W


On 18/07/2012, Ladd <ladd at codemettle.com> wrote:
> Is there a recommended way to remove events from working memory that don't
> match and can't activate any rules?
>
> For example, let's say I have two rules which should both fire when a
> person
> with name "Bob" is encountered.  If a person with name "Jim" comes in he
> stays in working memory forever even though he doesn't match any current
> rules.
>
> I know @expires() for Person events would work.  But I don't know what a
> "safe" time would be since I don't know ahead of time what temporal rules
> might be written for them.
>
> >From the 5.4.0 Drools Fusion docs (Chapter 2) I found these statements:
>
> /"In other words, one an event is inserted into the working memory, it is
> possible for the engine to find out when an event can no longer match other
> facts and automatically retract it, releasing its associated resources."/
>
> /"Events may be automatically expired after some time in the working
> memory.
> Typically this happens when, based on the existing rules in the knowledge
> base, the event can no longer match and activate any rules. Although, it is
> possible to explicitly define when an event should expire."/
>
> Based on this statement I would expect my "Jim" to be automatically expired
> after "some time".  Maybe it will be and I'm just not waiting long enough.
>
> But then I found this quote from Edson:
>
> /"Any object type for which there are no explicit
> expiration policy, nor temporal constraints from which to derive the
> expiration offset will have an infinite expiration offset, i.e., will never
> be automatically retracted."/
>
> So my question is, how can I retract events which don't match any rules?
>
> Thanks in advance for any tips or suggestsions!!
>
> - Ladd
>
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