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

[Simon Chen]

Let me make sure I get it correctly...

The example you gave seems to be the one-hop case. For the two-hop
case, we need something like this

when
   edge(a, b), reach(b, c), not exists reach(a, c)
then
   insertLogical( reach(a,c) )

So, where do you put your logical around? It should include both
edge(a,b) and reach(b,c), right?

Another thought, can we have something like
testExistsAndInsertLogical() to replace insertLogical()? But this may
be buggy, as the conditions are all met, so the rule actually fired...

I really need this working, so I'll probably take a crack at modifying
drools, although haven't done it before...

Thanks.
-Simon

On Saturday, February 19, 2011, 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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