Deniela:

As stated before, which you might not have seen, most of the problems with newbies and rulebased systems is that the process is declarative rather than procedural as with most other languages. When a rule is refracted (removed from the agenda permanently because it has already) the rule that is deleted is the rule+data, meaning that the same rule logic may appear several times but with a different set of data. If the data are changed, then the rule logic might appear again.


Now, to goal-oriented rules. Normally, in most rulebased systems, recency is one of the first items to consider. So, if a new goal is asserted it will take precedence over any other goals. That's why the goal usually appears as the first condition in the rule. The manner in which the rules are processed is not like other languages; it is determined as an abstract problem and is solved by the conflict resolution strategy. And, yes, under the covers, each OR is broken down into two rules complete with data associated with that rule.

Here is a fairly easy way to think of the rules: All of the rules and all of the data are put into a big pot. Each rule associates itself with a set of data and becomes an object. When we use goal- oriented rules, we restrict each set of rules to only those with the current goal - which can change if any of the rules assert another goal.

During the first cycle, all of the rules+data are examined (1) to associated each datum with a specific rule, (2) to associate a rule with specific data and (3) to see if any of the rules evaluate to TRUE. All of the rules that evaluate to TRUE are put on the Agenda Table as well as being put into a truth maintenance table. Then the rules are evaluated according to conflict resolution. If any datum is changed then any rule that used that datum is RE-evaluated to see if (1) it was false and is now true and it will be put on the Agenda table or (2) if it was true and on the Agenda table and is now false it will be removed. ONLY those rules where the data are changed are evaluated. And numerous tests over the years have determined that even with thousands of rules, only two or three rules are changed during one cycle of rules. Meaning that not all of the rules need to be checked - only those who data have changed.

I know that all of this might seem a bit low-level and simplistic, but sometimes we tend to forget that rules are "kind of" data driven - it's also sometimes called forward chaining which may or may not be a misnomer. Above all, read the book on Jess, "Jess in Action", and go through the examples and tutorials before attempting to design your own system.

If I sound condescending, I apologize but it's most difficult to answer questions over the internet without sounding like a professor talking to a student. If this has been of any help, good. If not, then just toss it. :-)

SDG
jco

James C. Owen
Senior Consultant
[EMAIL PROTECTED]
http://www.kbsc.com
"Never give up.  Never give up.  Never, never, never give up."
From a speech by former Prime Minister, Winston Churchill, during the most trying times of the British Empire; a great leader too soon forgotten by his country after keeping it from being swallowed up by the Nazi Empire during the second world war.



On Jan 25, 2006, at 2:51 AM, Daniela CLARO wrote:

Thank you Ernest,
I have more questions about it...The first one is that I'd read that Jess memorizes each rule that it passes and so Jess doesn't pass two times in the
same rule. Am I right?

If yes, in Monkey and Bananas example, I do not understand why it changes the goal in some actions, because for me the goal in a planner should be allways the same, for example eat bananas and as the planner is running and
passing to into rules, it will not fire that rule again.

If a rule has the OR operator, then as you said it creates another rule, and see below what it does. Actually, I thought that changing the goal in each action is the only way to make sure Jess will fire this rule only one time, but...how about the others solutions, how can I get them? Imagine that we
have these rules:
(clear)
(deffacts start
        (fermetureFenetre pose)
        (fermeturePorte pose)
        (fauxPlafond pose)
        (exist cloison)
)
(reset)

(defrule peindre-murs-et-plafonds
        (fermetureFenetre pose)
        (fermeturePorte pose)
        (fauxPlafond pose)
        (exist cloison)
=>
        (assert (murPlafond peint))
        (printout t "Peint murs et plafonds" crlf)
)

(defrule fournir-poser-papier-peint
        (murPlafond peint)
=>
        (assert (papierPeint pose))
        (printout t "Fourniture et pose des Papiers Peint" crlf)
)

(defrule peindre-sol
        (or (murPlafond peint) (papierPeint pose))
=>
        (assert (sol peint))
        (printout t "Peint le sol" crlf)
)

(defrule fournir-poser-moquette
        (sol peint)
        (or (murPlafond peint) (papierPeint pose))
=>
        (assert (moquette pose))
        (printout t "Fourniture et pose de moquette" crlf)
)
(run)

My answers are:
Peint murs et plafonds
Fourniture et pose des Papiers Peint
Peint le sol
Fourniture et pose de moquette
Fourniture et pose de moquette
Peint le sol
6

And then as Jess consider &1 as another rule, it did not stop at the first "Fourniture et pose de moquette" but it tries to execute the OR operator and fire the rule "Fourniture et pose de moquete" and "Peint le sol" two times.

Thus is it the reason that I should change the goals in each rule to assure that Jess will fire only one time each rule even if I have an OR operator?
Thus my answer in the first planner would be like that:
Peint murs et plafonds
Fourniture et pose des Papiers Peint
Peint le sol
Fourniture et pose de moquette


This order is fixed based on the preconditions, but imagine that X can be executed before Y or before Z. Thus how can I force that the first plan shows me X before Y and than another plan shows me X before Z. How can I get
the other plan?


Here is the watch all from
Jess> (batch peinture.clp)
 ==> Focus MAIN
 ==> f-0 (MAIN::initial-fact)
 ==> f-1 (MAIN::fermetureFenetre pose)
 ==> f-2 (MAIN::fermeturePorte pose)
 ==> f-3 (MAIN::fauxPlafond pose)
 ==> f-4 (MAIN::exist cloison)
==> Activation: MAIN::peindre-murs-et-plafonds :  f-1, f-2, f-3, f-4
MAIN::peindre-murs-et-plafonds: +1+1+1+1+1+1+1+2+1+1+1+2+1+1+1+2+t
MAIN::fournir-poser-papier-peint: +1+1+1+1+t
MAIN::peindre-sol: =1=1=1=1+t
MAIN::peindre-sol&1: +1+1+1+1+t
MAIN::fournir-poser-moquette: +1+1+1+1=1=1=1+2+t
MAIN::fournir-poser-moquette&1: =1=1=1=1=1=1=1+2+t
FIRE 1 MAIN::peindre-murs-et-plafonds f-1, f-2, f-3, f-4
 ==> f-5 (MAIN::murPlafond peint)
==> Activation: MAIN::fournir-poser-papier-peint :  f-5
==> Activation: MAIN::peindre-sol :  f-5
Peint murs et plafonds
FIRE 2 MAIN::fournir-poser-papier-peint f-5
 ==> f-6 (MAIN::papierPeint pose)
==> Activation: MAIN::peindre-sol :  f-6
Fourniture et pose des Papiers Peint
FIRE 3 MAIN::peindre-sol f-6
 ==> f-7 (MAIN::sol peint)
==> Activation: MAIN::fournir-poser-moquette :  f-7, f-5
==> Activation: MAIN::fournir-poser-moquette :  f-7, f-6
Peint le sol
FIRE 4 MAIN::fournir-poser-moquette f-7, f-6
 ==> f-8 (MAIN::moquette pose)
Fourniture et pose de moquette
FIRE 5 MAIN::fournir-poser-moquette f-7, f-5
Fourniture et pose de moquette
FIRE 6 MAIN::peindre-sol f-5
Peint le sol
 <== Focus MAIN
6
Jess>

Thank you!!!
Daniela

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