A Use Case Model describes the proposed functionality of a new system. A Use Case represents a discrete unit of interaction between a user (human or machine) and the system. This interaction is a single unit of meaningful work, such as Create Account or View Account Details. Use Cases provide the detailed view of the requirements. They do not specify ‘how' the solution will be developed. They provide a high-level flow that will need to be considered in product design but do not attempt to design the actual product. Each Use Case describes the functionality to be built in the proposed system, which can include another Use Case's functionality or extend another Use Case with its own behavior.