[rules-users] some basic questions to grouping

Tue Aug 19 12:06:17 EDT 2008

Jakob, Edson, thanks a lot for your replies especially on agenda vs
activation-group :)

But please allow me to ask some further questions:
1. The LHS of the rules is evaluated at "assert time".
When is actually the RETE network built? On assertion, will a fact then be
propagated over the network?

2. The example with Gender and countryOfBirth:
    For the gender example, you said the condition will be executed only
twice. So I assumed it's because there are 2 possibilities of gender. But
the example with countryOfBirth with 100 possibilities, why only once?

3. Back to my problem I described before:
   Before I read your reply (Edson's), I try to follow the suggestion from
Jakob, namely using the ruleflow-group. So I came up with a the
ruleflow-graph I attached (please have a look if you don't mind)
http://www.nabble.com/file/p19053522/regulation-check.rfm
regulation-check.rfm . I try to describe the following hierarchy:
There are certain rules only for young people; if they are older, than it
will be checked, whether he/she is a male/female. Another group of rules is
only valid for females, the rest of the rules are valid for both male and
female. does the graph correspond correctly to the problem I describe? Is it
better to use such grouping or like you said, just write my patterns and
constraints as much as possible (without the grouping)?
Again thanks in advance!

Regards

Edson Tirelli-3 wrote:
> 
> 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 at 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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>>
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> 
> 
> 
> -- 
> Edson Tirelli
> JBoss Drools Core Development
> JBoss, a division of Red Hat @ www.jboss.com
> 
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> 
> 

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