UML & Modeling • Use Case DiagramsEasy⏱️ ~2 min
What are Use Case Diagrams?
Definition
Use Case Diagrams are UML (Unified Modeling Language) behavioral diagrams that capture functional requirements by showing interactions between actors (users or external systems) and the system's use cases (specific functionalities or services the system provides).
Use Case Diagrams answer the fundamental question: What can users do with this system? They serve as a bridge between stakeholders who understand the business domain and developers who will implement the system. Unlike class diagrams that show structure, use case diagrams focus on behavior and user goals.
Core Components:
First, Actors represent roles that interact with the system (Customer, Admin, Payment Gateway).
Second, Use Cases represent specific functionalities (Book Parking Spot, Generate Invoice, Cancel Reservation).
Third, Relationships show how actors interact with use cases and how use cases relate to each other.
First, Actors represent roles that interact with the system (Customer, Admin, Payment Gateway).
Second, Use Cases represent specific functionalities (Book Parking Spot, Generate Invoice, Cancel Reservation).
Third, Relationships show how actors interact with use cases and how use cases relate to each other.
Interview Tip: When asked to design a system, always start with use case identification before jumping to class diagrams. This demonstrates requirements gathering skills and ensures you understand the problem domain.
When to Use: Use case diagrams are most valuable during the requirements phase and initial design discussions. They help identify missing functionality and clarify scope. However, they should not replace detailed behavioral modeling (sequence diagrams or activity diagrams) for complex workflows.
💡 Key Takeaways
✓Use case diagrams capture functional requirements by showing actor-system interactions
✓They focus on 'what' the system does, not 'how' it does it
✓Primary components are actors (roles), use cases (functionalities), and relationships
✓Serve as communication tools between stakeholders and development teams
✓Should be created before detailed class design to ensure proper scope understanding
📌 Examples
1Parking Lot System: Actors include Customer, Attendant, and Payment Gateway; use cases include Park Vehicle, Pay Fee, Generate Ticket
2Library System: Actors include Member, Librarian, and System; use cases include Borrow Book, Return Book, Search Catalog, Pay Fine
3Elevator System: Actors include Passenger and Maintenance Staff; use cases include Request Floor, Emergency Stop, Schedule Maintenance