Use Case Diagram Examples

Use case diagrams show interactions between actors (users, systems) and use cases (functionality) within a system boundary.

Simple ATM System

A classic use case diagram showing a bank customer interacting with an ATM.

DSL Code

diagram: use-case
title: "Simple ATM Example"

# Actor
actor User "Bank Customer"

# System
system-boundary ATM "ATM System" {
  ellipse-wide Withdraw "Withdraw Cash"
  ellipse-wide CheckBalance "Check Balance"
  ellipse-wide PrintReceipt "Print Receipt"
}

# Relationships
User -> Withdraw
User -> CheckBalance
Withdraw -> PrintReceipt "optional"

Generated SVG

Key Concepts

Actors: Represent users or external systems

• Use actor <ID> "<Label>" syntax
• Rendered as stick figures

System Boundaries: Container for use cases

• system-boundary <ID> "<Label>" { ... }
• Groups related functionality

Use Cases: System functionality

• ellipse-wide <ID> "<Label>"
• Oval shapes for actions

Relationships: Connections between actors and use cases

• Simple: Actor -> UseCase
• Labeled: UseCase1 -> UseCase2 "stereotype"

Banking System with Stereotypes

Advanced example showing UML stereotypes for include/extend relationships.

DSL Code

diagram: use-case
title: "Advanced Banking System"

# Actors
actor Customer "Bank Customer"
actor Admin "System Admin"
actor BackOffice "Back Office"

# System boundary
system-boundary Banking "Online Banking" {
  # Core use cases
  ellipse Login "Login"
  ellipse ViewAccount "View Account"
  ellipse Transfer "Transfer Money"
  ellipse PayBills "Pay Bills"

  # Extended use cases
  ellipse TwoFactor "Two-Factor Auth"
  ellipse ValidateAccount "Validate Account"
  ellipse SendNotification "Send Notification"
  ellipse AuditLog "Audit Log"
}

# Actor relationships
Customer -> Login
Customer -> ViewAccount
Customer -> Transfer
Customer -> PayBills

Admin -> AuditLog
BackOffice -> ValidateAccount

# Include relationships (mandatory)
edge Login -> TwoFactor stereotype: "<<include>>" lineStyle: dashed arrowType: open
edge Transfer -> ValidateAccount stereotype: "<<include>>" lineStyle: dashed arrowType: open
edge PayBills -> ValidateAccount stereotype: "<<include>>" lineStyle: dashed arrowType: open

# Extend relationships (optional)
edge SendNotification -> Transfer stereotype: "<<extend>>" lineStyle: dashed arrowType: open
edge SendNotification -> PayBills stereotype: "<<extend>>" lineStyle: dashed arrowType: open

UML Stereotypes

<<include>>: Mandatory behavior

• The base use case requires the included use case
• Example: Login requires Two-Factor Auth
• Use stereotype: "<<include>>" with lineStyle: dashed

<<extend>>: Optional behavior

• The base use case may use the extending use case
• Example: Transfer may trigger SendNotification
• Use stereotype: "<<extend>>" with lineStyle: dashed

Line Styles

# Solid line (default)
Actor -> UseCase

# Dashed line (for stereotypes)
edge UseCase1 -> UseCase2 stereotype: "<<include>>" lineStyle: dashed arrowType: open

# Dotted line
edge UseCase1 -> UseCase2 lineStyle: dotted

# Custom colors
edge UseCase1 -> UseCase2 strokeColor: "#4caf50" lineStyle: dashed

E-Commerce System

A more complex example with multiple actors and relationships.

DSL Code

diagram: use-case
title: "E-Commerce Platform"

# Actors
actor Visitor "Guest User"
actor Customer "Registered User"
actor Seller "Product Seller"
actor Admin "Administrator"

# System boundary
system-boundary Shop "E-Commerce System" {
  # Guest capabilities
  ellipse Browse "Browse Products"
  ellipse Search "Search Products"
  ellipse ViewDetails "View Product Details"

  # Customer capabilities
  ellipse Register "Register Account"
  ellipse Login "Login"
  ellipse AddCart "Add to Cart"
  ellipse Checkout "Checkout"
  ellipse Payment "Process Payment"
  ellipse TrackOrder "Track Order"

  # Seller capabilities
  ellipse ListProduct "List Product"
  ellipse ManageInventory "Manage Inventory"
  ellipse ViewSales "View Sales"

  # Admin capabilities
  ellipse ManageUsers "Manage Users"
  ellipse ViewAnalytics "View Analytics"
}

# Guest interactions
Visitor -> Browse
Visitor -> Search
Visitor -> ViewDetails
Visitor -> Register

# Customer interactions (inherits Guest + more)
Customer -> Login
Customer -> AddCart
Customer -> Checkout
Customer -> TrackOrder

# Seller interactions
Seller -> ListProduct
Seller -> ManageInventory
Seller -> ViewSales

# Admin interactions
Admin -> ManageUsers
Admin -> ViewAnalytics

# Include relationships
edge Checkout -> Payment stereotype: "\u003c\u003cinclude\u003e\u003e" lineStyle: dashed arrowType: open
edge ListProduct -> ManageInventory stereotype: "\u003c\u003cinclude\u003e\u003e" lineStyle: dashed arrowType: open

Actor Styles

Runiq provides 8 actor shapes for different visualizations:

actor User1 as @actor              # Classic stick figure
actor User2 as @box-actor          # Simplified box
actor User3 as @circle-actor       # Circle head with body
actor User4 as @rounded-actor      # Rounded corners
actor User5 as @square-actor       # Square body
actor User6 as @tall-actor         # Tall proportions
actor User7 as @wide-actor         # Wide proportions
actor User8 as @custom-actor       # Configurable

Best Practices

Actor Placement

• Place primary actors (users) on the left
• Place secondary actors (systems, admins) on the right
• Group related use cases within system boundaries

Stereotypes

• <<include>>: When behavior is always required
  • Login → Two-Factor Auth
  • Checkout → Process Payment
• <<extend>>: When behavior is optional
  • Transfer → Send Notification
  • Purchase → Apply Coupon :::

Relationship Lines

• Solid line: Actor to use case (standard association)
• Dashed line with arrow: Stereotype relationships (include/extend)
• Label on arrow: Describe the relationship type

Use Case Diagram Checklist

• [ ] Identify all actors (users, external systems)
• [ ] Define system boundary (what's inside your system)
• [ ] List all use cases (system functionality)
• [ ] Connect actors to their use cases
• [ ] Add <<include>> for mandatory shared behavior
• [ ] Add <<extend>> for optional enhancements
• [ ] Use meaningful labels for all elements
• [ ] Group related use cases logically

Next Steps

• Container Diagrams → - C4 architecture
• Flowcharts → - Process flows
• Shape Reference → - Actor shape options

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Download Examples

All example .runiq files are available in the GitHub repository.

git clone https://github.com/jgreywolf/runiq.git
cd runiq/examples/use-case-diagram