[rules-users] Misunderstanding salience?

[Peter Ashford]

Hi There

 

I'm new to drools.  I've just set up the Drools-Server and it is (finally!) working and serving my test rule-set.  The one thing that's not working as I expect it is the rule ordering via salience.  This is my simple test rule set:

 

rule "General brain eating advice"

       when

              p : Patient(eatsBrains == true)          

       then

              p.setAdvice("Stop eating brains, or at least, try to cut down");     

end

 

rule "Zombie exception to brain eating advice" 

       salience -50

       when

              p : Patient(eatsBrains == true, isZombie == true)

       then

              p.setAdvice("Evidence suggests that the undead cannot contract Kuru or that the effects are irellevant given the " +

                              "patient's current zombified state.\nSuggest euthenasing patient lest he/she eat your (or someone " +

                              "else's) brains");             

end

 

 

The idea is that the first rule fires all the time unless the patient happens to be a zombie, in which case the exception rule (the second rule) kicks in.  Now, as I have it here, with the exception at salience at -50 it actually works, which is the opposite of what I was expecting.  I'd thought that I would have had to have the exception at a higher salience to fire first.  That was what I tried first but that didn't work - everyone got the general advice, zombies included.

 

What am I misunderstanding here?

 

Thanks!

 

Peter.

 

---

"It is very difficult to get a man to understand something when his tribal identity depends on his not understanding it" - Michael Bérubé on Republican climate change denial.

 

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