[rules-users] accumulate / collect behaviour question - another stupid question

[Anstis, Michael (M.)]

I think you have misunderstood (or at least one of us has!)

The "transaction consistency" rule consists of four patterns:-
1 - Transaction ( $id : id) pattern. 
2 - The "$credit : Double() from..." pattern
3 - The "$debit : Double() from..." pattern 
4 - eval( ! $credits.equals( $debits ) )

The rule will only be activated when all patterns match. IMO, I think of
"accumulate" as a nested rule: the "action" will fire when the pattern
following the "accumulate (..." matches. Therefore pattern 2 above is
matched when the "accumulate" returns - i.e. it is always matched. The
same for patterns 1 and 3. Pattern 4 is only matched when the credits
and debits don't equal.

So for 100 Transaction facts and 10 TransactionEntry facts per each of
10 unique id's the rule will be activated once per pattern 4 match.
Pattern 1 always matches; pattern 2 always matches and pattern 3 always
matches. Although pattern matches 100 times, pattern 2 matches 10 times
per id and pattern 3 matches 10 times per id. I think it is different to
consider pattern matches versus rule activations.

I hope this helps!??! - or I'm completely wrong ;-)

Cheers,

Mike


-----Original Message-----
From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Olenin,
Vladimir (MOH)
Sent: 22 February 2007 14:52
To: Rules Users List
Subject: RE: [rules-users] accumulate / collect behaviour question -
another stupid question

> So, you are right: action will be executed 10 times for each id and
eval 
> will be executed 1 time for each id.

Hmm... So, the 'action' part of the _rule_ (NOT of the accumulate
statement)
will be called 100 times? How should the rule be modified for the action
to
be called only 10 times? (once per each unique transaction id).
Basically
the idea is to do smth if all debit operations are not balanced with
credit
operations within the same transaction id....

Or have I misunderstood





-----Original Message-----
From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Edson Tirelli
Sent: 21 February 2007 17:19
To: Rules Users List
Subject: Re: [rules-users] accumulate / collect behaviour question -
another
stupid question

  Vlad,

Inside an accumulate CE, the action code will be executed once for each 
match of the given pattern (TransactionEntry in this case).
Eval CEs are executed once for each tuple that matches all previous 
patterns.
So, you are right: action will be executed 10 times for each id and eval

will be executed 1 time for each id.

To understand better how forward rule engines work, there are some books

and articles listed in JBoss Rules project page. I can personally 
recomend "Expert Systems..." by Gary Riley.

And don't worry about asking. Usually people ask a lot in the begining 
and then when they feel confident, they start to answer more than ask.
:)

[]s
Edson

Olenin, Vladimir (MOH) wrote:

> Hi,
>
> Edson quoted the following sample rule some time ago:
>
> rule "transaction consistency"
>
> when
>
> Transaction( $id : id )
>
> $credits: Double( )
>
> from accumulate( TransactionEntry( id == $id, operation == "credit", 
> $amount : amount ),
>
> init( double balance = 0 ),
>
> action( balance += $amount ),
>
> result( new Double( balance ) ) );
>
> $debits: Double( )
>
> from accumulate( TransactionEntry( id == $id, operation == "debit", 
> $amount : amount ),
>
> init( double balance = 0 ),
>
> action( balance -= $amount ),
>
> result( new Double( balance ) ) );
>
> eval( ! $credits.equals( $debits ) ) then
>
> // inconsistency for transaction $id
>
> End
>
> If there are 100 transactions overall and only 10 unique transaction 
> ids (eg, id = 1..10), so that we have on average 10 Transaction facts 
> per id,
>
> - how many times will 'eval' be called?
>
> - how many times will the action be called, assuming 'eval' always 
> returns 'true'?
>
> I guess the answer for the above should be '10 times', once per each 
> id? What if I put another eval statement like "eval($id == 1)" after 
> existing 'eval'? Would that be evaluated 100 times (for all 
> Transaction facts) or only 10 times (once per unique id)?
>
> I think I'm missing quite significant piece on how tuples are selected

> in DROOLS and how 'eval' and new 'from accumulate' features work....
Any 
> pointers would be greatly appreciated! (would some general literature 
> on rule engines help to clear up this types of questions?...)
>
> Thanks,
>
> Vlad
>
> PS: sorry for posting so many questions and answering so few.....
>
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>
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>  
>


-- 
 Edson Tirelli
 Software Engineer - JBoss Rules Core Developer
 Office: +55 11 3124-6000
 Mobile: +55 11 9218-4151
 JBoss, a division of Red Hat @ www.jboss.com


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