1. A method in a computer system for determining whether a behavior represented by a role object in memory should be dynamically associated to a simulated entity represented by a cluster object in memory, comprising: at the cluster object, invoking a function thereof to pass the role object thereto; at the cluster object, under control of the function invoked, determining by the cluster object as to whether the behavior represented by the passed role object should be associated to the simulated entity; at the role object, invoking a function thereof, such that under control of the function invoked, determining by the role object as to whether the behavior represented by the role object should be associated to the simulated entity; ONLY after so determining, BOTH by the cluster object AND by the role object, indicating that the behavior represented by the passed role object should be associated to the simulated entity.