Use case diagrams in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the primary actor in a use case diagram

In a use case diagram for an online bookstore, which of the following is the primary actor?

A The customer who buys books

B The database storing book information

C The payment gateway service

D The server hosting the website

💡 Hint

Think about who initiates the interaction with the system.

The primary actor is the user or entity that interacts directly with the system to achieve a goal. Here, the customer is the primary actor because they initiate buying books.

❓ Architecture

intermediate

Determine the correct use case relationship

Which option correctly describes the include relationship in use case diagrams?

A Actors inherit behaviors from other actors

B A use case always calls another use case to reuse its behavior

C Two use cases are unrelated and independent

D A use case extends another use case optionally

💡 Hint

Consider which relationship means mandatory reuse of behavior.

The include relationship means one use case always uses the behavior of another use case to avoid repetition.

❓ scaling

advanced

Scaling use case diagrams for large systems

When designing use case diagrams for a large banking system, which approach best helps manage complexity?

A Only model the most important use cases and ignore others

B Create one large use case diagram with all actors and use cases

C Divide the system into subsystems and create separate use case diagrams for each

D Use sequence diagrams instead of use case diagrams

💡 Hint

Think about how to keep diagrams clear and understandable.

Dividing into subsystems and creating separate diagrams keeps each diagram focused and easier to understand.

❓ tradeoff

advanced

Tradeoffs in actor identification

What is a common tradeoff when deciding how many actors to include in a use case diagram?

A More actors make the diagram simpler but less detailed

B Fewer actors reduce clarity but increase diagram size

C Actors do not affect diagram complexity

D Too many actors can clutter the diagram and confuse readers

💡 Hint

Consider how visual clutter affects understanding.

Including too many actors can make diagrams crowded and hard to read, reducing their usefulness.

❓ component

expert

Analyzing request flow from use case to system components

In a use case diagram for a ride-sharing app, the 'Request Ride' use case involves the Rider actor and triggers several system components. Which sequence best represents the request flow from the actor to components?

A Rider → Authentication Service → Ride Matching Service → Payment Service

B Rider → Ride Matching Service → Authentication Service → Payment Service

C Rider → Payment Service → Ride Matching Service → Authentication Service

D Rider → Payment Service → Authentication Service → Ride Matching Service

💡 Hint

Think about the logical order of verifying identity, matching rides, then processing payment.

The rider must first be authenticated, then the system matches a driver, and finally processes payment.