Use Case Diagrams

What is the Use Case diagram?

Use Case Diagram captures the system’s functionality and requirements by using actors and use cases.

Use Cases model the services, tasks, function that a system needs to perform.

Use Cases represent high-level functionalities and how a user will handle the system.

Use Cases are the concepts of Unified Modelling language modelling.

Use Cases — Horizontally shaped ovals that represent the different uses that a user might have.

Actors — Stick figures that represent the people actually employing the use cases.

Associations — A line between actors and use cases. In complex diagrams, it is important to know which actors are associated with which use cases.

System boundary boxes — A box that sets a system scope to use cases. All use cases outside the box would be considered outside the scope of that system.

Packages — A UML shape that allows you to put different elements into groups. Just as with component diagrams, these groupings are represented as file folders.

Tips for drawing a Use Case Diagram

A use case diagram should be as simple as possible.

A use case diagram should be complete.

A use case diagram should represent all interactions with the use case.

If there are too many use cases or actors, then only the essential use cases should be represented.

A use case diagram should describe at least a single module of a system.

If the use case diagram is large, then it should be generalized.

Advanced Use Case Modelling

Concepts Extension use case

A use case consisting of steps extracted from a more complex use case in order to simplify the original case is called an extension use case.

It is represented as an arrow-headed line beginning at the extension use case and pointing to the use case it is extending. The relationship line is labelled “<<extends>>.”

Abstract use case

Abstract use case reduces redundancy among two or more other use cases by combining the common steps found in those cases.

An abstract case is available for use by any other use case that requires its functionality.

It is depicted as an arrow-headed line beginning at the original use case and pointing to the use case it is using. Each relationship line is labelled “<<uses>>.”

Examples