Ans: Action is a simple non-decomposable piece of the overall behavior that is being modeled. On the other hand, an activity is used to represent a set of actions. An activity can further be decomposed into other activities or actions. Actions and activities can represent both computerized or manual behavior. They are depicted using rounded rectangles. Object nodes model objects in the activity diagram. They are represented using rectangles. Object nodes represent the flow of information from one activity to another activity. Response: See pages 160-162