[rules-users] Why Using "from" Always Return A New Fact?

I am trying to understand why care should be taken to use "from" and "lock-on-active" together, as is described in "Section 4.8.3.8. Conditional Element from" of http://downloads.jboss.com/drools/docs/5.1.1.34858.FINAL/drools-expert/ht... the Drools Reference Document . It says "the use of from returns a new fact for all intents and purposes each time it is evaluated." Why is it true? Below is the full related-text copied from the Drools Reference Document for your reference: === BEGIN === You must take caution, however, when using from, especially in conjunction with the lock-on-active rule attribute as it may produce unexpected results. Consider the example provided earlier, but now slightly modified as follows: rule "Assign people in North Carolina (NC) to sales region 1" ruleflow-group "test" lock-on-active true when $p : Person( ) $a : Address( state == "NC") from $p.address then modify ($p) {} #Assign person to sales region 1 in a modify block end rule "Apply a discount to people in the city of Raleigh" ruleflow-group "test" lock-on-active true when $p : Person( ) $a : Address( city == "Raleigh") from $p.address then modify ($p) {} #Apply discount to person in a modify block end In the above example, persons in Raleigh, NC should be assigned to sales region 1 and receive a discount; i.e., you would expect both rules to activate and fire. Instead you will find that only the second rule fires. If you were to turn on the audit log, you would also see that when the second rule fires, it deactivates the first rule. Since the rule attribute lock-on-active prevents a rule from creating new activations when a set of facts change, the first rule fails to reactivate. Though the set of facts have not changed, the use of from returns a new fact for all intents and purposes each time it is evaluated. === END === -- View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/Why-Using-from-Always... Sent from the Drools - User mailing list archive at Nabble.com.