[rules-users] duration attribute & other rule language features issue

[Wolfgang Laun]

It seems that a full definition of the semantics of @expires is still
missing from the Fusion manual.

"After that time, assuming no rule *still needs the event*, the engine will
expire and remove the event from the session automatically." (Emphasis by
me.)

So, when does a rule "need an event"? This is a very iffy definition.

Consider:
   when
      Event()
   then
This rule certainly "needs" an Event fact, but does it still need it after
the first firing? Not unless Event() is modified, which might happen
elsewhere.

In the case of a timer() being added to a rule, there is a similar dilemma.
A rule like
  rule
    timer(int: 5s)
  when
    Event()
  then
does and, simultaneously does not, "need" an Event() fact. If Event() is
retracted after less than 5s, the rule should not fire - so the rule does
not "need" the fact. OTOH, its timed firing depends on the presence of an
Event() - so the rule "needs" the fact.

You can easily thwart the algorithm that determines "is needed":

rule "check timer attribute"
    timer (int: 5s 1s)
when
    $alert : Object( eval($alert instanceof Alert) ) from entry-point
"EventStream"
then
     System.out.println( ((Alert)$alert).getId() +
                        " time: " +
(Calendar.getInstance().getTimeInMillis()));
end

-W



On 28 November 2011 07:32, prashant.badhe <prashant.badhe at gmail.com> wrote:

> Here is the complete rule that we trying out with 'timer' & '@expires' :
>
> ~~~~~~~~~~~~~
> package xyz;
>
> import abc.Alert;
> import abc.CResult;
>
> import java.util.regex.Matcher;
> import java.util.regex.Pattern;
> import java.util.ArrayList;
> import java.util.HashMap;
> import java.util.Iterator;
> import java.util.Date;
> import java.util.Calendar;
> import java.util.Timer;
>
> declare Alert
>        @role( event )
>        @expires( 30s )
> end
>
> declare CResult
>        @role( event )
>        @expires( 30s )
> end
>
> rule "check timer attribute"
>        agenda-group "xyz"
>        auto-focus true
>        no-loop
>        salience 140
>               timer (int: 5s)
>        //duration ( 5s )
>
>        when
>                $alert : Alert( $alertId:id ) from entry-point "EventStream"
>        then
>                System.out.println("Inside RHS...[alert=" + $alert.getId()
> + "]
> [Time: " + (Calendar.getInstance().getTimeInMillis()));
>
> end
> ~~~~~~~~~~~~~
>
> We are trying this out on Drools 5.3.0 stateful knowledge session operating
> in stream mode.
>
> The above rule is not firing on inserting Alert fact. If I comment line
> 'timer (int: 5s 5s)' then it starts firing.
>
> About the @expires, our assumption is Alert fact inserted is not expiring,
> as the count returned by getFactCount() on WM entrypoint object is returned
> as 1 even after a thread sleep of more than 60 seconds post the rule
> firing.
>
> Please correct us if this assumption is wrong or something more is required
> for @expires to work. Similarly for timer(int: 5s) let us know what is
> wrong.
>
> Does the facts that are expired remains in WM but are not evaluated for any
> new facts/rules inserted in WM OR they are removed from WM?
>
> -Prashant
>
>
>
>
> --
> View this message in context:
> http://drools.46999.n3.nabble.com/rules-users-duration-attribute-other-rule-language-features-issue-tp3536857p3541469.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
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