Hello all,
I would like to suggest we return to the beggining here to explore
interesting ways for a football manager and coaches to use JBRules. :)
First of all, lets define a possible object business model. Lets
start with a single class (pseudo code):
class Player {
String name;
String position;
int skill; // how good the player is: grade from 0 to 10.
int age;
double salary;
// getters and setters
}
Ok, so, we have a set of players asserted into working memory. Lets
say now, the manager asks the coach to define who will be the main team
for the next season, and the coach wants to use his best player for each
position. A rule like this one could be used:
global java.util.List mainTeam;
rule "Main Team"
$player: Player( $name: name, $skill: skill, $position: position)
not Player( position == $position, skill > $skill )
then
System.out.println(" The best player for position
"+$player.getPosition()+" is "+$player.getName() );
mainTeam.add($player);
end
So, using this single rule, the coach will cast his best player for
each position.
Now, lets say, all tournments have age constraints. So, the coach
wants to know his best team for each tournment, matching age
constraints. So, lets improve our business model to allow Tournments to
be defined:
class Tournment {
String name;
int minimumAge;
int maximumAge;
List team;
// getters and setters
}
So, now, we can change our rule to take tournments into account:
rule "Team for each tournment"
$tournment : Tournment( $minAge: minimumAge, $maxAge: maximumAge )
$player: Player( $name: name, $skill: skill, $position: position, age
>= $minAge, age <= $maxAge )
not Player( position == $position, skill > $skill, age >= $minAge,
age <= $maxAge )
then
$tournment.addPlayerToTeam( $player );
end
As you can see by above examples, it is always good to define rules
in terms of our business model and usually not use "hardcoded"
constraints. This will make for clear and more maintainable rules, as
well as avoid an "infinite" sequence of nested "or" and "and" operators.
What if a team must be under a certain total salary cost? What if
players can't join more than X silmultaneous tournments? It is always
simple and straightforward to define this kind of rule, as long as you
have a good business model with supporting data.
Having said that, JBRules does support nested "or" and "and"
operators (though it does not support "not" with nested operators inside
it), but it is important to note that the top level "or" operator in
rules engines (this is not JBRules specific) will effectivelly create
multiple rules in the backend. So, if you say:
rule "A"
ClassX(<constraints>) || ClassY( <constraints> )
then
..
end
It is only syntax sugar, as it will compile to:
rule "A1"
ClassX(<constraints>)
then
..
end
rule "A2"
ClassY( <constraints> )
then
..
end
If you have a complex sequence of nested "and" and "or" operators, it
will use Morgan's theorem to transform it in a disjunction of
conjunctions, i.e., a top level "or" with "and"s beneath it. After that,
it will break the "or" making each logical branch a single subrule.
Again, this is not JBRules specific, but general rules engine's behavior.
Sorry for the long e-mail, but I hope this brings some light to the
subject under discussion, i.e., I hope our football managers and coaches
continue to use JBRules and winning tournments! ;)
Let me know if you guys have any question or issue you would like to
discuss further, and thanks for bringing some fun and good humor to the
list!
[]s
Edson
John Cocktolstoy wrote:
First - thanks for answers.
So, basically I could use evaluation such as:
Player1 ( hisage : age -> ( compare(hisage, 19, 21) ) )
or even, without the inline function:
Player1 ( hisage : age -> ( (age == 19) || (age == 21)) ) )
This is equivalent to what Matias did although he put it into dsl.
As to what is stated in documentation, it indeed suggest that man can
create rule like in algebra with grouping and nesting "and"s and
"or"s. From my experience it all work as long as you don't nest.
regards
John
On 11/8/06, *gabriel quennesson* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
That's why I said It probably wasn't the answer you expected.
You could use an inline function that would compare the value and
return
true if it matches one argument or the other :
when
Player1 ( hisage : age -> ( compare(hisage, 19, 21) ) )
then
doStuff();
end
function boolean compare(int age, int firstValue, int secondValue) {
if (age == firstValue)
return true;
if (age == secondValue)
return true;
return false;
}
But I must admit it is not very clean either.
Now, in drools doc section * 3.23 *it is stated you can group using
parenthesis and keywords, pretty much like you would in algebra. I
abandoned the idea though, and did the same by writing several rules.
John Cocktolstoy a écrit :
> Thanks for the answer!
> Yep, in case of String types I could use 'matches' . But what if
each
> player have also field:
> int age
> and instead of names I would like to compare age of players? How to
> cope with that?
>
> As to the second idea - I think I can't just write the rule the
exact
> way I did with "and" and "or" keywords. I believe it is
impossible to
> nest "and"s and "or"s. Am I right? I also wasn't able to
successfully
> write such a rule.
>
> regards
> John
>
> On 11/8/06, *gabriel quennesson*
<[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>
> <mailto: [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>> wrote:
>
> I'm not sure this is the answer you expect but you could do the
> following :
>
> when
>
> Player1 (name matches "Roy|Bob")
>
> Player2(name matches "Tom|Eric")
>
> ...
>
> Player11(name matches "Paulo|Ryan")
>
> then
>
> doStuff();
>
> end
>
>
>
> In some trickier cases, you could use functions to perform other
> forms of matching.
>
> Or you could just write the rule the exact way you did with
"and"
> and "or" keywords, which is documented in Drools (I wasn't
able to
> successfully write such a rule, though).
>
> Regards,
>
> Gabriel
>
> John Cocktolstoy a écrit :
>> Hi,
>>
>> I am new to Drools, I just read documentations and went through
>> some examples.
>> I am wondering about the following example (I spiced it up
with a
>> story so it should not be boring :-) ):
>>
>> Suppose I am a football manager and trying to use Drools to
>> automate some processes.
>> I have 11 classes (these are going to be facts):
>> Player1, Player2, Player3, ..., Player11
>> One for each player of my team, each of class has one field:
>> String name
>> In run-time I will assert into working memory only one instance
>> of each class as I would like to evaluate some rules over my
>> current team.
>> Now I would like to create simple rule - I express it in
>> pseudo-language:
>>
>> when
>> ((Player1.name <http://Player1.name>
<http://player1.name/> == "Roy") or (
>> Player1.name <http://Player1.name> <http://player1.name/>
== "Bob"))
>> and
>> ((Player2.name <http://Player2.name>
<http://player2.name/> == "Tom") or (
>> Player2.name <http://Player2.name> <http://player2.name/>
== "Eric"))
>> and
>> ...
>> and
>> ((Player11.name <http://Player11.name>
<http://player11.name/> == "Paulo") or
>> (Player11.name <http://Player11.name>
<http://player11.name/> == "Ryan"))
>> then
>> do something
>>
>> Could anyone show me how to express this rule using Drools
>> without going into huge number of rules? As I understand from
>> documentation each 'or' is creating two sub-rules. Isn't that
>> limitation that makes Drools useless for football managers?
>>
>> regards
>> John
>
>
--
___________________
*Gabriel Quennesson *| CTC/I | *SEAM*
Int :* *7 906 6910 | Ext: 04 73 64 69 10
[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>
<mailto:[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>
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