[rules-users] Drools and threads

Hi I have few questions about Drools. Are rules compiled, partially compiled or interpreted ? When I call fireAllRules(), does it ( or can it ) create a new thread that runs parallely or the operation is sequential and the caller program HAS TO wait till all rules execution is done ? Also, How is the application data integrity guarantied? E.g. what happens when some of the facts are changed in middle of rules being executed .. ? what should happen ? -abhay