UML Diagrams MCQs Questions With Answers – Part 21

April 20, 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. In a UML activity diagram, what does a guard condition represent?

A A logical test applied before an event occurs.

B A condition that decides if an activity is accepted in a workflow.

C A constraint written in brackets [ ] on a transition, used to determine the path to follow.

D A loop of activities repeated indefinitely.

Guards (or guard conditions) are boolean expressions, written as [condition], on the outgoing arrows of a decision node. They control the path taken after an activity, like an if statement in a program. Example:

A system moves through different states depending on the value of a variable x:

If x ≤ 10 → go to Normal state
If x > 10 → go to Alert state

2. In an activity diagram, what does a diamond with several outgoing arrows represent?

A A loop

B A conditional decision

C A terminal state

D A subprocess

The diamond represents a choice between multiple paths based on a condition. Example:

3. You want to model the repeated execution of an action (e.g., login attempt). Which combined fragment should you use?

A opt

B alt

C loop

D ref

The loop fragment allows you to repeat a sequence as long as a condition is true (e.g., max 3 attempts). Example:

4. What is the difference between a synchronous and an asynchronous message in a UML sequence diagram?

A A synchronous message never returns a response.

B An asynchronous message blocks the sender until it receives a reply.

C A synchronous message waits for a response; an asynchronous one does not.

D There is no difference in UML.

A synchronous message (solid line with closed arrowhead) blocks the sender until the operation ends (like a method call). An asynchronous message (solid line with open arrowhead) does not block; the sender continues its processing. Example:

5. This diagram represents __________

A A relationship between objects in the same program

B Software components and their interactions in an architecture

C The relationship between an application and a database

D A relationship between a class and its interface

This diagram shows software components in a system architecture, where Server interacts with Database.

6. What does this diagram represent?

A Concrete instances of the Client class

B An abstract Client class

C Objects in a class diagram

D Objects in an object diagram representing specific instances

The diagram shows specific objects (client1, client2), representing concrete instances of classes in an object diagram.

7. What does the OCL (Object Constraint Language) allow you to express in UML?

A Logical interfaces for components.

B Visual styles for UML diagrams.

C Precise constraints on UML models such as invariants, preconditions, or postconditions.

D User interaction scripts.

OCL is a declarative language used to specify precise rules in a UML model. It is often used to express invariants (always true), preconditions (before an operation), or postconditions (after).

8. In UML, what is multiple generalization?

A A child class that inherits from a single parent class.

B A child class that inherits from multiple parent classes.

C A class that inherits from an entire package.

D An interface that inherits from a concrete class.

Multiple generalization in UML means that a class can inherit from multiple classes, which can be useful but should be used with caution (conflict issues or the “diamond problem”). Example:

9. You are building an e-learning system. What UML relationship between a course and its chapters if the chapters exist only with the course?

A Aggregation

B Association

C Dependency

D Composition

If the course is deleted, the chapters disappear too → composition.

10. What does the relationship Student <--> Course mean?

A A Student can be enrolled in several Courses, but a Course can have no Students.

B A Student can be enrolled in only one Course.

C A Course must have at least one enrolled Student.

D A Student cannot be enrolled in multiple Courses.

The multiplicity 1 and 0..* means a Student can enroll in multiple Courses, but a Course may have no Students.

1. In a UML activity diagram, what does a guard condition represent?

2. In an activity diagram, what does a diamond with several outgoing arrows represent?

3. You want to model the repeated execution of an action (e.g., login attempt). Which combined fragment should you use?

4. What is the difference between a synchronous and an asynchronous message in a UML sequence diagram?

5. This diagram represents __________

6. What does this diagram represent?

7. What does the OCL (Object Constraint Language) allow you to express in UML?

8. In UML, what is multiple generalization?

9. You are building an e-learning system. What UML relationship between a course and its chapters if the chapters exist only with the course?

10. What does the relationship Student <--> Course mean?

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