Fundamentals of UML Diagrams

1.3. A Use Case Diagram

Use cases are versatile and valuable techniques for describing user requirements. A use case is a high-level description of a major user requirement. It represents the functionality of the system. It is a description of the system’s behaviour from a user’s viewpoint and constitutes a complete interaction with the system initiated by a user or another system. 

Use case diagrams address the static use case view of a system. The different types of people and/or devices (called actors) that interact with the system are identified along with the functions that they perform or initiate. A Use Case diagram shows a set of use cases and actors (a special kind of class) and their relationships.

These diagrams are especially important in organizing and modelling the behaviors of a system. They are valuable aid during analysis, since developing Use Cases helps to understand requirements. Use Cases and a Conceptual Model are the powerful techniques in requirement analysis. Notations used when representing use case diagrams include:

Basic Use Case Notation 

The Actor represents a user of the system, or any external system that interacts with the system. The Use case represents a piece of functionality that is important to the user. Mostly we see the actor as a human user, but it can also represent a system or other nonhuman artifact. Figure 2.4 shows the basic notation of a use case diagram.

Figure 2.4: Basic Notation of a Use Case Diagram