[rules-users] Plz reply : Descending order rule

[Edson Tirelli]

   Barath,

   Your mistake is treating NOT as a boolean operator instead of existential
quantifier.
   In other words: NOT is an EXISTENTIAL quantifier. It will be true only if
there are no facts that satisfy your pattern. So, the rule engine will bind
a fact to the first pattern and will try to match the existential quantifier
NOT against all existing facts:

Case 1 :   $a : Order($value : 1)
              not Order( value > 1)

           So match is false because there are Orders whose value are 2 and
3.

Case 2 :   $a : Order($value : 2)
              not Order( value > 2)

           So match is false because there is an Order whose value is 3.

Case 3 :   $a : Order($value : 3)
              not Order( value > 3)

           So match is TRUE because there are NO Orders whose value is
greater than 3.
           Rule will fire and retract Order( value : 3)

Case 4 :   $a : Order($value : 2)
              not Order( value > 2)

          Now, this match is true, because there are no more Orders whose
value is greater than 2, since Order( value : 3 ) was retracted in the
previous step.

         And so on...

        Hope it helps,
         Edson


2008/2/21, Barath <barathguna at gmail.com>:
>
>
> Hi,
>
> I apologize for my logic fault i made in previous post.
>
> The correct logic as follows,
>
>
> rule "Descending order"
>     when
>         $a : Order( $value : value )
>         not Order( value > $value)
>     then
>         System.out.println("value :"+$value);
>         retract($a);
> end
>
> 1. Order value=1
>
> 2. Order value=2
> 3. Order value=3
>
>
> Case 1 :   $a : Order($value : 1)
>               not Order(2 > 1)
>
>            So rule is False.
>
>
> Case 2 :   $a : Order($value : 1)
>               not Order(3 > 1)
>
>            So rule is False.
>
>
> Case 3 :   $a : Order($value : 2)
>
>               not Order(1 > 2)
>            So rule is True.
>
>
> Case 4 :   $a : Order($value : 2)
>
>               not Order(3 > 2)
>            So rule is False.
>
>
> Case 5 :   $a : Order($value : 3)
>
>               not Order(1 > 3)
>            So rule is True.
>
>
> Case 6 :   $a : Order($value : 3)
>
>               not Order(2 > 3)
>            So rule is True.
>
>
> This indicates the rule should fire for three times but its not the case.
> I know i going wrong some where but i couldn't figure out.
> Plz do help me.....
>
> Barath.
>
> --
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>
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>
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-- 
  Edson Tirelli
  JBoss Drools Core Development
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com
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