Use Case Diagram

Definition

A Use Case Diagram is an UML diagram that aims to present a statement of functionality required of a system (e.g. software). The units of functionality that the system provides for its users are called use cases.

It is a type of behavioral diagram that enables the definition of requirements that a system must fulfill. The diagram describes which users use which functionalities of the system. It does not address specific details of an implementation.

A use case describes functionality expected from the system. It may encompas a number of functions that happen (are performed or executed) when using a system. A use case provides a tangible benefit for one or more (entities) actors.

In general, a use case is triggered either by invocation (stimulus) of an actor or by a trigger event.

PlantUML Elements

A PlantUML use case diagram specifies and shows the following:

• An Actor represents a requirement (stimulus) of the system
• An Action representing a capability of the system
• A Subject representing the item acted upon by an Action of the system

Example

@startuml
'https://plantuml.com/sequence-diagram

autonumber

Payer -> Payee: Payment 
Payee --> Payer: Payment Confirmation

Payer -> Payee: Another Payment
Payee --> Payer: Another Payment Confirmation
@enduml

References

• Sequence Diagram @ Wikipedia
• PlantUML Language Reference Guide