Mastering UML Use Case Diagrams: A Practical Guide for Architects

UML Use Case Diagram

UML use case diagram, English name Use Case Diagram, is a type of UML diagram mainly used to describe actors and the connections between actors and use cases.

UML use case diagram describes system functions from the user’s perspective. Its main purposes are: 1) to identify who uses the system; 2) to show what those users can do with the system.

This perspective helps understand business, express requirements clearly, and assists developers in implementing the described elements.

UML Use Case Diagram Components

The diagram consists of actors, use cases, system boundaries, and relationships, as illustrated below.

1. Actor

Actor represents a user, organization, or external system that interacts with the system, typically depicted as a stick figure.

2. Use Case

Use Case is an externally visible system function that describes the service provided by the system, usually shown as an ellipse.

Use cases are commonly expressed as “verb noun” to indicate what the system can do, such as login app, place order, or make payment.

3. System Boundary

System Boundary separates the inside of the system from the outside; actors are placed outside, use cases inside, typically represented by a rectangular box.

A well‑defined product has clear boundaries, specifying what is included and what is excluded.

UML Use Case Diagram Example

Consider a mobile phone recharge service where a recharge app is needed to allow users to top up their balance.

The corresponding UML use case diagram is shown below.

Creating a UML use case diagram helps analyze the business scenario, clarify requirements, and progressively derive system functionalities.