UML Use Case Diagram

Question 1

Use Case Diagram:

What is a Use Case?

Answer 1

A formal way of representing how a system interacts with its environment.

• Illustrates activities performed by users of the system
• Scenario-based technique in UML
• Emphasis on what a system does, not how
• Describes what a system does from the standpoint of an external observer

Question 2

Use Case Diagrams:

Components

Answer 2

• Scenarios
• Actors
• Actions (use case)
• Communications
• Relations

Question 3

Use Case Diagrams:

What is a Scenario?

Answer 3

An example of what happens when someone interacts with the system.

Should describe:

• The starting situation/state of the system
• The normal flow of events
• Possible ways an interaction can go wrong
• Information about other concurrent activities
• The state of the system when the scenario finishes

Question 4

Use Case Diagrams:

Relations

Basic Description

Answer 4

Relations are a technique for categorizing the various Actors and Use Cases.

Represented as lines ending with arrows.

Three Types:

• Generalization
• Extend
• Include

Question 5

Use Case Diagrams:

Three Types of Relations

Answer 5

Generalization

Extend

Include

Question 6

Use Case Diagrams:

Relations:

Generalization

Answer 6

Indicates that something is a specialized type.

Can apply to Actions or Actors.

Represented by a forked line, with a white arrow pointing to the more general thing. Similar to inheritance.

Examples:

• Pressing the ‘Esc’ key is a a specialized version of the more general action of pressing a key
• A “New Patient” Actor is a specialized version of the more general “Patient” Actor

Question 7

Use Case Diagrams:

Relations:

Extend

Answer 7

Used when a case conditionally adds steps to another first class use case.

Represented with a plain arrow from one case to the other, marked with <>

Question 8

Use Case Diagrams:

Relations:

Include

Answer 8

Used to extract use case “fragments”, which are duplicated in multiple use cases.

Represented with a white arrow pointing to the Fragment that will be included, with the line marked with

<>

Question 9

Use Case Diagrams:

Actor

Summary

Answer 9

An Actor is a user or outside system, which interacts with the system being designed in order to obtain some value from that interaction.

Use Cases describe the interaction between Actors and the system itself.

Actors can be humans, machines, external systems, sensors, etc

Question 10

Steps for

Designing a Use Case

Answer 10

Repeat for all potential use cases

1. Identify the Actors
2. Identify the Use Case
3. Diagram the communication
4. Determine the System Boundary