Use Case Diagram (UCD)

This article is a definition of terms for Use Case Diagram (UCD) – including exam questions, core components, and tags.

In a Nutshell

A Use Case Diagram models from a user’s perspective which objectives actors achieve with a system and which use cases the system offers. It is an important artifact of requirements analysis.

Compact Technical Description

A UCD shows:

• Actors (roles/external systems) outside the system boundary
• System boundary (scope)
• Use cases (goal-oriented application scenarios)

Relations:

• include: mandatory reuse (always required)
• extend: optional extension under condition
• Generalization: specialization of actors/use cases

UCD describes the what, not the how. Details belong in textual use case descriptions (triggers, pre-/postconditions, main/alternative scenarios) and in sequence/activity diagrams.

For security, misuse cases can be used.

Exam-Relevant Key Points

• Goal level, no technical UI clicks
• Actors are roles outside the system boundary
• include vs extend (IHK frequently tests this)
• Derive requirements, acceptance criteria, and tests from UCD
• Misuse cases for threats
• Diagram + text description versioning/approval

Core Components

1. Primary/secondary actors
2. System boundary
3. Use case (ellipse)
4. Association actor ↔ use case
5. include
6. extend
7. Generalization
8. External systems
9. Misuse case
10. Traceability (use case → test)

Practical Example (Web Shop)

Actors: Customer, Payment Provider, Admin
Use Cases: Register, Sign In, Search Product, Shopping Cart, Pay
Pay: include Start Payment Process
Pay: extend Apply Discount (if voucher)
Misuse: Unauthorized Access → Countermeasure 2FA

Advantages and Disadvantages

Advantages

• Very good stakeholder communication
• Clear system boundaries
• Good basis for requirements and test derivation

Disadvantages

• No detailed process logic
• Risk of overload
• Text descriptions are additionally required

Typical Exam Questions (with Short Answers)

1. What is a UCD used for? Functional scope from user perspective + system boundary.
2. include vs extend? include = always required, extend = optional under condition.
3. What belongs in the textual use case description? Triggers, pre-/postconditions, scenarios, acceptance criteria.
4. How do you derive tests? Each scenario variant yields at least one test case.

Free Response

In the FIAE exam, “UCD” almost always means the Use Case Diagram (not User-Centered Design). Therefore, pay attention to correct notation, clear objective names, and the derivation of requirements and tests.

Learning Strategy

1. Sketch UCD for web shop.
2. Describe use cases textually (pre-/postconditions).
3. Practice include/extend.
4. Create traceability table use case → test case.

Most Important Sources

1. https://www.omg.org/spec/UML
2. https://de.wikipedia.org/wiki/Anwendungsfalldiagramm
3. https://alistair.cockburn.us/knowledgebase/writing-effective-use-cases/