What is a Use Case Diagram in UML?

What is a use case diagram in UML?

Use case diagrams are easy to create and read. Their purpose is to describe who uses your application or system, then model what the user can accomplish therein.

To draw your own use case diagram, just click the buttons below. It's intuitive and completely free—plus, you can access our application from nearly any device or operating system.

Try it now
Sign up free

What is a Use Case Diagram in UML?

In the Unified Modeling Language, a use case diagram can summarize the details of your system's users (also known as actors) and their interactions with the system. To build one, you'll use a set of specialized symbols and connectors. An effective use case diagram can help your team discuss and represent:

  • Scenarios in which your system or application interacts with people, organizations, or external systems
  • Goals that it helps those entities (known as actors) achieve
  • The scope of your system

Employing Use Case Diagrams

Remember that a use case diagram doesn't go into a great deal of detail—for example, don't expect it to model the order in which steps are performed. Instead, a proper use case diagram depicts a high-level overview of the relationship between use cases, actors, and systems. Experts recommend that use case diagrams be used to supplement a more descriptive textual use case.

UML is the modeling toolkit that you can use to build your diagrams. With a use case diagram, the use cases are symbolized with a labeled oval shape. Lines represent actors in the process, and the actor's participation in the system is modeled with a line between the actor and use case. To depict the system boundary, draw a box around the use case itself.

What is a use case diagram in UML?

When to Apply a Use Case Diagram

There's no need to be confused about the relevance of use case diagrams. They're ideal in situations such as:

  • Representing the goals of system-user interactions
  • Defining and organizing functional requirements in a system
  • Specifying the context and requirements of a system
  • Modeling the basic flow of events in a use case


To answer the question of "What is a use case diagram in UML?", you need to first understand its building blocks. Common components include:

  • Actors - the users that interact with a system. An actor can be a person, an organization, or an outside system that interacts with your application or system. They must be external objects that produce or consume data.
  • System - a specific sequence of actions and interactions between actors and the system. A system may also be referred to as a scenario.
  • Goals - the end result of most use cases. A successful diagram should describe the activities and variants used to reach the goal.
What is a use case diagram in UML?

Lucidchart comes with pre-made shapes for UML, including activity, sequence, and use case diagrams. It's easy to collaborate in real-time with your team—try it today and see!

Try it now
Sign up free