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

[Mark Proctor]

On 19/02/2011 15:01, Simon Chen wrote:
> 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...
I'm just thinking about what it is you want to do. Do you wan to 
pre-compute a matrix for fast lookup if C is reachable from A? Where the 
integrity of that matrix is maintained by logical insertions?

Or are you trying to do adhoc reachability with minimial maintained 
state, no pre-calculated state, where performance is not such an issue?

Mark
> 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
>>> _______________________________________________
>>> rules-users mailing list
>>> rules-users at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>
>>>
>>
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