[rules-users] unsolved myth regarding transitive closure using insertlogical...

[Mark Proctor]

I think to impl this what is needed is a "logical" node. At the moment 
the entire LHS forms the justification. But if we supported a logical 
node, we could do this:
rule "reachDirect"
     salience 10
     when
         logical( e : Edge(s1 : source, t1 : target) )
         not( Reach(source == s1, target == t1) )
     then
         insertLogical( new Reach(e.getSource(),e.getTarget()) );
         System.out.println( "Reach " + e.getSource() + "," + 
e.getTarget() );
end


That means that it would be inserted when there was no Reach, but it 
would only be retracted when there was no matching Edge. The 
justification is only for the part of the rule that is in the logical 
grouping.

To do this is actually quite a trivial change in drools, but it's not 
something we do now. I think one reason why I held off was that i was 
looking at Jess and Clips that have this and they state you can have 
multiple logical elements. But i could't figure out how having 2 or 3 
would differ, compare to having just one.

Anway to support a singe logical element, you'd need to update the 
parser to support 'logical' conditional element, in the same format as 
'not' and 'exists'. Then if you look at RuleTerminalNode you'll see the 
part of the code that is related to removing the justifications,  on a 
retract or modify - removeLogicalDependencies. Likewise if you look in 
the DefaultKnowlegeHelper you'll see how the insertion works. That could 
would instead be copied to the logical node. If a logical node exists 
the RTN should have an if statement so the same code does not execute again.

Any takers?

Mark


On 19/02/2011 05:20, Simon Chen wrote:
> Hi all,
>
> I know this is kinda an old topic, but I just couldn't get it working.
>
> Here is a previous attempt using insertLogical() to handle transitive
> closure:
> http://drools-java-rules-engine.46999.n3.nabble.com/transitive-closure-td56855.html#a56858
> The problem with this one is that the newly "logically inserted" object
> would violate its own "not exists" condition term, thus removing itself,
> then goes the infinite circle of insert/remove...
>
> Here is a post that deals with transitive closure using "insert", but it
> doesn't handle object removal correctly:
> http://drools-java-rules-engine.46999.n3.nabble.com/one-question-about-Transitive-Closure-td57289.html
>
>
> To me, using insertLogical is attractive because it doesn't require me to
> write specific rules to handle object removal. Is there a trick that I can
> use to actually implement transitive closure with insertLogical?
>
> Thanks a lot!
> -Simon
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