[rules-users] Dynamic facts

[Wolfgang Laun]

On 19 July 2011 13:42, Marc Heinz <marc.heinz at no-log.org> wrote:

>
> rule "Single rule check age"
> when
>        p : Person( age > 18 )
> then
>        System.out.println("Single rule fired");
> end
>
> rule "Rule 1 of n"
>    when
>        p : Person( name.equals("Adam") )
>    then
>        System.out.println("Rule 1 of n fired");
> end
>
> // [...] hundred of others similar rules that will perform a check on the
> // name attribute.
> =================================
>
> And with the following java code:
>
> Person p = new Person();
> p.setAge(22);
> p.setName("Adam");
> FactHandle fh = ksession.insert(p);
> ksession.fireAllRules();
> p.setAge(23);
> ksession.update(fh, p);
> ksession.fireAllRules();
>
> This will actually produce the output:
> Rule 1 of n fired
> Single rule fired
> Rule 1 of n fired
> Single rule fired
>
> So, despite I have only updated one attribute of the fact (the age of a
> Person), all rules have been fired again, even if they had nothing to do
> with the said attribute, which could possibly produce a huge overhead.
>
> I maybe misunderstood some basic concept here... But is there a way to
> prevent that?
>

Reevaluation of all patterns referring to the type of  a fact/object that
has been changed is a fundamental principle of production rule systems.

For example, I expect a different behavior when using a
> PropertyChangeSupport object that would fire events only for specific
> fields (but I wasn't able to test it yet)...
>

Reaction to a property change event is just
  wm.update( factHandle, object )

-W

>
> Thanks,
> Marc
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