[rules-users] Cutom Attributes in Drools

[GPatel at tsys.com]

"I would not store the result of the (missed) activation of a rule in a 
rule
attribute, anyway. Can't you just use a dedicated fact(s) for that?"

I face a similar issue where the target audience are "business" users i.e 
users that dont really understanding or wish to get into logic. I am 
finding myself having to resort to all sorts of tricks (using 
categories/packages/standlone rule editor) to allow business users to 
easily specify which rules are for what purposes and when they should 
fire. I just cant rely on them using facts correctly to disable rules that 
should not fire. In fact, I am now down to using only the standalone 
editor and saving the rule xml in my tables (not guvnor) so that i have 
full control over itemized rule display, rule search, knowledgebase 
creation for different execution profiles, etc.

Overall, I increasingly tend to think rules for business users is a myth. 
The business users wants rule-driven systems, yet they dont want to learn 
drools. And drools DSL just doesnt cut it.



From:   Davide Sottara <dsotty at gmail.com>
To:     rules-users at lists.jboss.org, 
Date:   09/13/2012 01:57 AM
Subject:        Re: [rules-users] Cutom Attributes in Drools
Sent by:        rules-users-bounces at lists.jboss.org



You can add any metadata using the format @name( "value" ) or @name(
key=value ). You can then look them up using rule.getMetaData(). 
Please notice that there's a bug (solved by an open pull request) that 
does
not let you write just @name.

In order to use those attributes to control whether a rule fires or not, 
you
can use the "declarative agenda", i.e. add meta-rules to your knowledge 
base
such as:

rule "Meta"
@activationListener('direct')
when
    // assuming the attribute is @region( [value] )
    $a : Activation( rule.metaData[ "name" ] != "MyDesiredRegion", $objs :
objects )
    // any condition on the tuple here, if needed
then
    drools.cancelActivation( $a );
end

notice that you'll have to enable the corresponding option first:
KnowledgeBaseConfiguration kconf =
KnowledgeBaseFactory.newKnowledgeBaseConfiguration();
kconf.setOption( DeclarativeAgendaOption.ENABLED );
KnowledgeBase kb = KnowledgeBaseFactory.newKnowledgeBase( kconf );


If you want to have rules override each other, watch out for an upcoming
feature, "Defeasible logic".
I would not store the result of the (missed) activation of a rule in a 
rule
attribute, anyway. Can't you
just use a dedicated fact(s) for that?

Best
Davide



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