Use Case Diagram

Introduction to Use Case Diagram

UML Use Case Diagrams can be used to describe the functionality of a system in a horizontal way. That is, rather than merely representing the details of individual features of your system, Use Case Diagrams can be used to show all of its available functionality. It is important to note, though, that Use Case Diagrams are fundamentally different from sequence diagrams or flow charts because they do not make any attempt to represent the order or number of times that the systems actions and sub-actions should be executed. There are a number of graphical examples in this FAQ; you might want to look over them to familiarise yourself with the look of them.

Use Case Diagrams have only 4 major elements:

·         the actors that the system you are describing interacts with

·         the system itself

·         the use cases, or services, that the system knows how to perform

·         the lines that represent relationships between these elements.

You should use Use Case Diagrams to represent the functionality of your system from a top-down perspective (that is, at a glance the system's functionality is obvious, but all descriptions are at a very high level. Further detail can later be added to the diagram to elucidate interesting points in the system's behaviour.)