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

[Salaboy]

I will take a look on those classes, sounds really interesting. 

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- Mauricio "Salaboy" Salatino -

On 19/02/2011, at 05:24, Mark Proctor <mproctor at codehaus.org> wrote:

> 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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>> 
>> 
> 
> 
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