1. when you are saying "rules fire", does this mean: matching/checking the
LHS of rule, or executing the RHS of rule
Means execute the RHS. The LHS of the rules is evaluated at "assert time". Take a look at the docs for more info on that.
2. I plan to use the grouping features of drools, but still not sure..
First a quick explanation:
* agenda-groups allow you to control in what order rules are **fired**, because only rules from the active agenda-group are allowed to fire.
* activation-groups allow you to create mutually exclusive rules, because when a rule in an activation-group **fires**, it cancel all other activations in the same group.
None of it is what you want. In fact, you should not worry about the cases you described. Just write your patterns and constraints in the same order as much as possible, and also always write more constraining patterns before the more general patterns and let the engine do its magic.
If you have 1 rule where gender is Gender.MALE, and 1000 rules where it is Gender.FEMALE and you assert a male (or female, dos not matter) Person, the engine will execute the condition only twice, because it shares the Gender.FEMALE constraint among all the rules, assuming you write the constraints in the same order. An even more interesting situation is: pretend you have some kind of discriminating attribute for person, like countryOfBirth, and you have 100 rules for each country that you have to handle (lets say 100). So, you have 100 x 100 = 10000 rules:
Rule x1 when Person( countryOfBirth == Country.CANADA...
...
Rule x500 when Person( countryOfBirth == Country.BRAZIL...
...
Guess how many times that condition will be executed for a Person whose country is CANADA (or any other country, does not matter)? Only **once**, because of an optimization called alpha hashing.
Now range conditions are not hashed, but they still have node sharing, so as long as you write them in the same order, they are still optimized. The only problem you will have is if you start using accumulate and collect, that are really expensive in terms of performance. In cases like that, you will need a manual optimization, but it is still doable.
Hope it helps.
Edson
2008/8/19 psentosa
<psentosa@yahoo.com>
Hi,
I'm having some difficulty to understand the concept of grouping, but maybe
it's only because of my understanding of the terms, so please apologize for
the silly question
1. when you are saying "rules fire", does this mean: matching/checking the
LHS of rule, or executing the RHS of rule
2. I plan to use the grouping features of drools, but still not sure
whether(and how) to use the agenda or activation group (or even the
rule-flow). My problem domain is actually quite simple:
- rules are applied based on e.g age of a person. Now, there are some rules
for 17-year-or older, and some for 30-year-old person, if I'm to use the
agenda group, I'd define the following:
rule1
agenda-group "17 years-old or older"
when
p:Person (Age > 17)
....
rule2
agenda-group "17 years-old or older"
when
p:Person (Age > 17)
.....
rule3
agenda-group "30 years-old or older"
when
p:Person (Age > 30)
......
rule4
agenda-group "30 years-old or older"
when
p:Person (Age > 30)
......
If I assert a person into the WM to check his/her age, I want that only the
rules in 30-years-old agenda are CHECKED (and eventually executed when the
other constraints are fulfilled), bcs they are surely older than 17 as well.
And this is not only for comparing ages. Another example, some rules are
only for Gender.MALE, and some only for Gender.FEMALE. So if a person is
asserted, only the rules with corresponding gender will be checked and no
need of checking/matching the other group
The main purpose is just to skip checking unrelevant rules (imagine if there
is only 1 rule for MALE and 1000 rules for FEMALE with 1000 times WHEN
person (gender == FEMALE) checking for an asserted male-object).
How can I do this effectively? Or will ALL rules checked and only the order
of checking (and eventually exection of their RHS) is defined by the
grouping?
I hope I've described my problem clearly and I'll try to explain this again
in case of difficulty :)
Thanks in advance
Regards
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Edson Tirelli
JBoss Drools Core Development
JBoss, a division of Red Hat @ www.jboss.com