[rules-users] Order of Execution on Messages

[Wolfgang Laun]

On 28/02/2012, gboro54 <gboro54 at gmail.com> wrote:
> We are currently authoring rules using Drools 5.3 and using jBPM 5.2 for
> orchestration. The situation we have is as follows: Certain groups of rules
> can execute on n number of messages in any order(i.e the order in which the
> consequences occur does not matter). The problem comes in later in the
> process when those same n messages need to have their consequences happen in
> a certain order. Is there a good way to handle this? We have thought about
> appending messages to a queue and just operating on one message at a time
> however this seems slow.

"seems" seems to be not from experience. How big is n, how slow is slow?
A simple test will tell you all.

Nevertheless, there may be relatively slow and relatively fast
techniques for achieving firing in order. (I assume that ordering the
results is not an alternative to "firing in order".)

(a) Use dynamic salience, provided there is some integer ordinal as a
field of Message.

(b) Use a class Container { List<Message> msgs } as a fact, containing
all Messages in msgs. Insert Container as fact. Assuming your rules
run at salience 0 or higher:

rule nextMessage
salience -100
when
    Container( $msgs: msgs, eval( $msgs.size() > 0 ) )
then
    insert( msgs.remove( 0 ) );
end

rule noMoreMessages
salience -100
when
    $cont: Container( $msgs: msgs, eval( $msgs.size() == 0 ) )
then
   retract(  $cont );
end

(This is a good example for the rule design pattern "Proxy Facts".)

-W

> In addition when utilizing jBPM and drools what is
> the best way to batch data in and out of the session. I understand starting
> a new session is cheap but was hoping there may be a way to have jBPM insert
> n records at a time and just continue to read from the db until no more
> records are returned.
>
> TIA!
>
>
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