• (A) The low-level components of a system are integrated and tested before the higher-level components have been developed
• (B) The testing process starts with modules at lower levels in the hierarchy and works up the hierarchy of modules until the final module is tested.
• (C) An event driven control system, where an event is broadcasted to each sub- system and any sub-system that can handle that event responds to it.
• (D) Control starts of the top of a sub routine hierarchy and through sub routine calls passes to lower levels.