Interaction diagrams are used to model the dynamic aspects of a software system They help you to visualize how the system runs. An interaction diagram is often built from a use case and a class diagram. —The objective is to show how a set of objects accomplish the required interactions with an actor
The process by which a software engineer learns about the domain to better understand the problem: The domain is the general field of business or technology in which the clients will use the software A domain expert is a person who has a deep knowledge of the domain