UML Diagrams MCQs Questions With Answers – Part 4

April 19, 2025 John Howard

Test your knowledge and boost your confidence with these multiple-choice quizzes focused on UML diagrams, foundational software engineering concepts, and real-world best practices. Designed for students, developers, and exam candidates, these MCQs offer a quick and effective way to assess your understanding and sharpen your skills.

1. What is the main difference between aggregation and composition?

A There is none

B Composition implies a stronger shared lifetime

C Aggregation does not allow use of objects

D Aggregation is always used with interfaces

In a composition, the relationship is strong: if the main object is destroyed, the “contained” object is also destroyed. In aggregation, this is not necessarily the case. Example:

2. In UML, a simple line between two classes generally represents:

A An association

B A dependency

C A generalization

D A state transition

An association is a simple relationship between two classes (e.g.: a customer can book one or more flights). It is represented by a simple line, possibly with multiplicity (1..*, 0..1, etc.). Example:

3. Which UML diagram is used to model the dynamic behavior of a system by showing object interactions over time?

A Use case diagram

B Sequence diagram

C Class diagram

D Activity diagram

The sequence diagram emphasizes the chronological order of messages exchanged between objects to carry out a specific use case. Example:

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4. In a sequence diagram, what is a “lifeline”?

A A type of arrow

B An abstract class

C A vertical axis representing an object

D A state transition

A lifeline is a vertical line that represents the existence of an object over time, in a sequence diagram. Messages (arrows) are exchanged between these lifelines. Example:

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5. What type of diagram is shown in the image below?

A Class diagram

B Use case diagram

C Sequence diagram

D Activity diagram

This diagram shows an actor (“Customer”) interacting with two use cases: “Order a product” and “Pay for the order”. It illustrates system behavior from the user’s perspective.

6. What do the “+” and “-” symbols before attributes and methods represent?

A Nothing special, just style decorators

B Syntax errors

C “+” for method, “-” for attribute

D Visibility level: “+” for public, “-” for private

In UML, “+” means public, “-” means private, “#” would mean protected.

7. What is the purpose of a sequence diagram?

A Show class hierarchy

B Illustrate the evolution of an object over time

C Describe time-based interactions between objects

D Describe a system’s database

This diagram shows the order of messages exchanged between entities (actors, classes, systems) in a given scenario.

8. What are the rectangles that appear on lifelines during processing called?

A Actions

B Components

C Combined fragments

D Activation (or control focus)

An activation (or “control focus”) is a rectangle on a lifeline that indicates when an object is executing an operation. It shows the start and end of a method. Example:

A Client object calls the method pay() on an Invoice object. During this method’s execution, an activation is shown as a rectangle on Invoice’s lifeline.

9. UML is mainly used during which phase of software development?

A Maintenance phase

B Deployment phase

C Analysis and design

D Unit testing

UML (Unified Modeling Language) is primarily used during the analysis and design phase of software development to visually model the structure and behavior of a system before implementation. It helps in understanding requirements, designing architecture, and communicating ideas among stakeholders.

10. What is the correct way to represent “zero to many” multiplicity in a UML association?

A 0..0

B 0..*

C ..

D 1..*

In UML, 0..* means “zero or more” instances. It indicates that a class can be linked to none, one, or many instances of another class. Example:

One Book is owned by one or more Libraries. A Library can own zero or more Books.

1. What is the main difference between aggregation and composition?

2. In UML, a simple line between two classes generally represents:

3. Which UML diagram is used to model the dynamic behavior of a system by showing object interactions over time?

4. In a sequence diagram, what is a “lifeline”?

5. What type of diagram is shown in the image below?

6. What do the “+” and “-” symbols before attributes and methods represent?

7. What is the purpose of a sequence diagram?

8. What are the rectangles that appear on lifelines during processing called?

9. UML is mainly used during which phase of software development?

10. What is the correct way to represent “zero to many” multiplicity in a UML association?

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