[rules-users] need design suggestion

[Wolfgang Laun]

See inline.

On 02/04/2012, Joe Zendle <jzendle at zentechinc.net> wrote:
>
>
> Here are my rules:
>
> rule "card going down"
>     when
       // There is a Card in state UP and...
>     $card : Card($name : name , state == State.UP)
      // a matching notification to DOWN
>         $notif : Notification( id == $name, type == NotificationType.CARD ,
> state == State.DOWN )
>     then
>     System.out.println("  got notification for card down " + $card );
>     modify($card) {
>     setState(State.DOWN);
>     }
>     retract($notif);
> end
>
> // is the following rule correct??

No.

>
> rule "port going down"
>     when

     // There is a Port in State UP and...

>     $port : Port($name : name , state == State.UP, $card : card)
     // ...take its Card and if this is DOWN

>         Card ( state == State.DOWN) from $card
>     then
>     System.out.println("  port down because card is down  port: " + $port +
> " card: " + $card );
>      modify($port) {
>     setState(State.DOWN);
>     }

The difference between these two rules is that the first one is triggered by
a change in WM - the emergence of a matching Notification. The second,
however, is evaluated when the Port enters WM, presumably with its
Card in working order. Subsequently, Port doesn't change and so evaluation
is never retried.


Two correct versions:

when
$card : Card( state == State.DOWN )
$port : Port($name : name , state == State.UP, card == $card)
then

when
$port : Port($name : name , state == State.UP, $card: card )
           Card( this == $card, state == State.DOWN )
then

Or, assuming that Port must follow Card, for going UP and DOWN:

when
$card : Card( $stateCard: state )
$port : Port($name : name , state != $stateCard, card == $card)
then
modify($port) {
    setState($stateCard)
}


>
> end
>
> Here is the test case in a nutshell:
>
>  Port port1 = new Port();
> Port port2 = new Port();
>                         port1.setName("port1");
>  port2.setName("port2");
>
>                         Card card1 = new Card();
> card1.setName("port1 card1")
>                         port1.setCard(card1);
>                        // stateful session
>                         ksession.insert(port1);
> ksession.insert(port2);
> ksession.insert(card1);
>
> System.out.println("  firing rules");
> new Thread(new Runnable() {
> public void run() {
> ksession.fireUntilHalt();
> }
> }).start();
>
> System.out.println("*** injecting notification down");
> Notification notif = new Notification();
> notif.setType(NotificationType.CARD);
> notif.setState(State.DOWN);
> notif.setId("port1 card1");
> FactHandle notifHandle = ksession.insert(notif);
>
>
>                         ksession.halt();
>                         ksession.dispose()
>
>
> I would expect the card down notification to cause the port to do down by
> the second rule above but it does not fire.
>
> Here is output
>
>   card1: Card [state=UP, name=port1 card1,
> ne=org.plugtree.examples.model.NE at 1e2670b]
> OBJECT ASSERTED value:Port [state=UP, name=port1, card=Card [state=UP,
> name=port1 card1, ne=org.plugtree.examples.model.NE at 1e2670b]] factId: 1
> OBJECT ASSERTED value:Port [state=UP, name=port2, card=Card [state=UP,
> name=port1 card1, ne=org.plugtree.examples.model.NE at 1e2670b]] factId: 3
> OBJECT ASSERTED value:Card [state=UP, name=port1 card1,
> ne=org.plugtree.examples.model.NE at 1e2670b] factId: 5
>   firing rules
> 3
> *** injecting notification down
> ACTIVATION CREATED rule:card going down activationId:card going down [6, 5]
> declarations: $name=port1 card1(5);
> $notif=org.plugtree.examples.model.Notification at 4a9a7d(6); $card=Card
> [state=UP, name=port1 card1, ne=org.plugtree.examples.model.NE at 1e2670b](5)
> OBJECT ASSERTED value:org.plugtree.examples.model.Notification at 4a9a7dfactId:
> 6
> BEFORE ACTIVATION FIRED rule:card going down activationId:card going down
> [6, 5] declarations: $name=port1 card1(5);
> $notif=org.plugtree.examples.model.Notification at 4a9a7d(6); $card=Card
> [state=UP, name=port1 card1, ne=org.plugtree.examples.model.NE at 1e2670b](5)
>   got notification for card down Card [state=UP, name=port1 card1,
> ne=org.plugtree.examples.model.NE at 1e2670b]
> OBJECT MODIFIED value:Card [state=DOWN, name=port1 card1,
> ne=org.plugtree.examples.model.NE at 1e2670b] factId: 5
> OBJECT RETRACTED
> value:org.plugtree.examples.model.Notification at 4a9a7dfactId: 6
> AFTER ACTIVATION FIRED rule:card going down activationId:card going down
> [-1, 5] declarations: $name=port1 card1(5); $card=Card [state=DOWN,
> name=port1 card1, ne=org.plugtree.examples.model.NE at 1e2670b](5)
>
>
>
> Is the second rule written incorrectly? or do i have a gap in my
> expectations of how the engine should work (or both)
>
> Thanks in advance,
>
> Joe.
>