Use Case Diagram – Actors, System Boundary, Include, Extend & Generalization

This article explains use case diagrams, covering the key concepts, exam questions, and related terminology.

In a Nutshell

A use case diagram illustrates what functionality a system offers from the perspective of its users (actors) and how those users interact with the system.

Core Definition

Use case diagrams are part of UML (Unified Modeling Language) and visualize the functional requirements of a software system. They show which actors interact with which use cases, with each use case representing a complete unit of system functionality. These diagrams are particularly valuable during the early stages of software development for requirements analysis and stakeholder communication. Relationships like include, extend, and generalization clarify dependencies between use cases. Actors can be real users or external systems.

Exam-Relevant Points

• Part of UML for requirements analysis
• Visualizes user and system interactions
• Consists of actors, system boundaries, and use cases
• Essential for specification documents and system design
• Facilitates communication with clients and end users
• Supports risk analysis through clear functional overview
• Can be applied early for effort estimation
• Requires proper documentation and version control

Key Components

1. Actor (e.g., user, external service)
2. System boundary
3. Use case
4. Include relationship
5. Extend relationship
6. Generalization between actors or use cases
7. System context definition
8. Interaction scenarios
9. Access control through role assignment
10. Review and testing against requirements documents

Practical Example

// Example: Web shop
Actor: Customer
Use cases: Create account, Log in, Place order
Relationship: "Place order" includes "Log in"

Explanation: A customer can only place an order after logging in. Therefore, "Log in" is a mandatory part of the "Place order" use case.

Strengths and Limitations

Strengths

• Promotes shared understanding
• Clear delineation of system responsibility
• Easy to visualize
• Early entry point for modeling

Limitations

• Lacks technical detail
• Limited suitability for complex workflows
• Risk of over-abstraction

Common Exam Questions (with Brief Answers)

1. What does a use case diagram represent? It shows which actors interact with which use cases of a system.

2. Difference between include and extend? Include mandates execution of a use case, while extend is optional and adds behavior on demand.

3. Elements in a use case diagram? Actors, use cases, system boundary, and relationships (include, extend, generalization).

4. Purpose of the system boundary? It separates the system from its environment and clarifies what belongs to the system.

5. Primary vs. secondary actor? Primary actors initiate the use case; secondary actors are required by the system.

6. Why use early in a project? Helps gather requirements and verify them with stakeholders.

7. How does it support quality assurance? Clear functional separation makes testing more straightforward.

8. How does it support security analysis? Identifies critical functions and access points for role-based controls.

Key Resources

1. https://www.omg.org/spec/UML/
2. https://www.visual-paradigm.com/guide/uml-unified-modeling-language/what-is-use-case-diagram/
3. https://www.ihk-aka.de/