Use Case Diagrams

📌 What is a Use Case Diagram?

A Use Case Diagram is a behavioral UML diagram that visually represents the interactions between users (actors) and a system's functionalities (use cases). It focuses on what the system does rather than how it does it.

Purpose:

• Capture functional requirements of a system.

• Illustrate system behavior as seen by external users.

• Identify key actors and their goals when interacting with the system.

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🎯 Key Elements of a Use Case Diagram

Element	Description	Symbol/Notation
Actors	Users or external systems interacting with system	Stick figure or name label
Use Cases	Functionalities/services provided by system	Oval shape with name inside
System Boundary	Shows scope of system	Rectangle enclosing use cases
Relationships	Connections between actors and use cases	Lines, arrows, include/extend arrows

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✅ Types of Relationships in Use Case Diagrams

Relationship	Description	Symbol
Association	Actor interacts with use case	Solid line
Include	Mandatory behavior included in another use case	Dotted arrow with <<include>> label
Extend	Optional/conditional behavior that extends another use case	Dotted arrow with <<extend>> label
Generalization	One actor inherits behavior from another (specialization)	Solid line with hollow arrow

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🧭 How to Create a Use Case Diagram (Step-by-Step)

1. Identify Actors: Who uses the system? (Users, other systems).

2. Identify Use Cases: What functionalities does the system provide?

3. Define System Boundary: What is inside vs. outside the system?

4. Establish Relationships: Connect actors to use cases, define dependencies.

5. Organize and Label Clearly: Keep diagram simple and readable.

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📊 Example of a Use Case Diagram

Scenario: Online Shopping System

Actors	Use Cases
Customer	- Browse Products - Add to Cart - Checkout - Track Order
Admin	- Manage Products - Manage Orders
Payment Gateway (System)	- Process Payment

Diagram Representation (Text version):

pgsqlCopyEdit            +---------------------------------------+
            |         Online Shopping System        |
            |                                       |
            |   (Browse Products)                   |
            |   (Add to Cart)                       |
            |   (Checkout) ----<<include>>-- (Process Payment)  |
            |   (Track Order)                       |
            |   (Manage Products)                   |
            |   (Manage Orders)                     |
            +---------------------------------------+
                ^             ^          ^
             Customer      Admin     Payment Gateway

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💡 Example Relationships Explained:

• Customer — Browse Products: Direct interaction (association).

• Checkout <<include>> Process Payment: Payment is mandatory during checkout.

• Admin — Manage Products/Orders: Admin role functionality.

• Payment Gateway — Process Payment: External system involved in transaction.

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🚀 Benefits of Use Case Diagrams

Benefit	Explanation
Clarifies Requirements	Shows system functionality and user interaction clearly.
Communicates Scope	Defines what is and isn't part of the system.
Enhances Stakeholder Communication	Visual representation helps non-technical stakeholders understand.
Foundation for System Design	A starting point for detailed functional requirements and user stories.

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🔑 Best Practices for Use Case Diagrams

• Keep diagrams simple and focused.

• Use clear, descriptive names for use cases.

• Limit number of elements to avoid clutter.

• Focus on main user goals and system interactions.

• Use include/extend relationships appropriately to avoid repetition.

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🎯 Summary of Use Case Diagrams

Aspect	Details
Purpose	Visualize user-system interaction, capture functional requirements
Key Elements	Actors, Use Cases, System Boundary, Relationships
Main Relationships	Association, Include, Extend, Generalization
Outcome	Clear understanding of what the system will do for different users