Requirements and use cases in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Functional vs Non-Functional Requirements

Which of the following is an example of a non-functional requirement in a system design?

A The system must allow users to reset their passwords via email.

B The system should support login using username and password.

C The system must store user profiles with name and email address.

D The system should respond to user requests within 2 seconds.

💡 Hint

Non-functional requirements describe how the system performs rather than what it does.

Option D describes a performance constraint, which is a non-functional requirement. The others describe specific features (functional requirements).

❓ Architecture

intermediate

Use Case Diagram Interpretation

Given a use case diagram with actors: User, Admin; and use cases: Login, Manage Users, View Reports, which use case is typically exclusive to the Admin actor?

A Manage Users

B All use cases are for both actors

C View Reports

D Login

💡 Hint

Think about which actions require higher privileges.

Managing users usually requires admin privileges, so only Admin can perform 'Manage Users'. Login and View Reports can be common to both.

❓ scaling

advanced

Estimating System Load from Use Cases

A system has 10,000 daily active users. The use case 'Upload Photo' is used by 20% of users daily, each uploading 3 photos on average. What is the estimated number of photo uploads per day?

A 6,000 uploads

B 30,000 uploads

C 200,000 uploads

D 600 uploads

💡 Hint

Calculate the number of users performing the action and multiply by average uploads.

20% of 10,000 users = 2,000 users. Each uploads 3 photos, so 2,000 * 3 = 6,000 uploads (Option A).

❓ tradeoff

advanced

Tradeoff Between Requirements and System Complexity

Adding a requirement for real-time notifications increases system complexity. Which is the best tradeoff approach?

A Ignore the requirement to keep system simple.

B Build a complex event-driven system from the start.

C Implement notifications with a simple polling mechanism initially.

D Delay notifications feature indefinitely.

💡 Hint

Consider starting simple and improving later.

Option C balances requirement fulfillment and complexity by starting with polling, which is simpler than event-driven systems.

❓ component

expert

Identifying Components from Use Cases

Given use cases: User Registration, Payment Processing, Order Tracking, which component should handle the 'Payment Processing' use case in a modular system?

A User Interface Component

B Payment Gateway Component

C Authentication Component

D Order Management Component

💡 Hint

Think about which component deals with money transactions.

Payment Processing is best handled by a dedicated Payment Gateway Component to isolate payment logic and security.

Practice

1. What is the main purpose of requirements in system design?

easy

A. To write the system's source code

B. To describe how users interact with the system

C. To design the user interface layout

D. To specify what the system must do

Solution

1. Step 1: Understand the definition of requirements

   Requirements define the functions and features the system must provide.

2. Step 2: Differentiate from use cases

   Use cases describe user interactions, not the system's core functions.

3. Final Answer:

   To specify what the system must do -> Option D

4. Quick Check:

   Requirements = system functions [OK]

Hint: Requirements = what system must do, not how users act [OK]

Common Mistakes:

• Confusing requirements with use cases
• Thinking requirements include UI design
• Assuming requirements are code instructions

2. Which of the following best describes a use case in system design?

easy

A. A scenario showing user interaction with the system

B. A code module for user authentication

C. A diagram of system architecture

D. A detailed list of system features

Solution

1. Step 1: Define use case

   A use case is a story or scenario describing how a user uses the system.

2. Step 2: Eliminate unrelated options

   System features list, architecture diagrams, and code modules are not use cases.

3. Final Answer:

   A scenario showing user interaction with the system -> Option A

4. Quick Check:

   Use case = user scenario [OK]

Hint: Use case = user story or interaction example [OK]

Common Mistakes:

• Mixing use cases with system features
• Confusing use cases with technical diagrams
• Thinking use cases are code components

3. Given a system that allows users to upload photos and comment, which of the following is a valid use case?

medium

A. System stores photos in a database

B. User uploads a photo and receives confirmation message

C. Database schema includes photo metadata fields

D. Server runs a nightly backup process

Solution

1. Step 1: Identify user actions in options

   User uploads a photo and receives confirmation message describes a user action and system response, fitting a use case.

2. Step 2: Recognize system internals vs user interaction

   Options A, C, and D describe internal system details, not user interactions.

3. Final Answer:

   User uploads a photo and receives confirmation message -> Option B

4. Quick Check:

   User action + system response = use case [OK]

Hint: Use case = user action plus system reaction [OK]

Common Mistakes:

• Choosing system internal processes as use cases
• Ignoring the user perspective
• Confusing data storage details with use cases

4. A system design document lists: "Users can reset passwords via email." Which of the following is a problem in this use case description?

medium

A. It includes too much technical detail about email servers

B. It lacks the steps describing how users reset passwords

C. It incorrectly describes a system requirement instead of a use case

D. It is missing the database schema for password storage

Solution

1. Step 1: Analyze the use case description

   The statement is a high-level feature but lacks detailed user steps.

2. Step 2: Understand use case completeness

   Use cases should describe user actions step-by-step, not just state features.

3. Final Answer:

   It incorrectly describes a system requirement instead of a use case -> Option C

4. Quick Check:

   Use case needs detailed user steps [OK]

Hint: Use cases must show user steps, not just features [OK]

Common Mistakes:

• Confusing requirements with use cases
• Expecting technical details in use cases
• Ignoring the need for step-by-step user actions

5. You are designing a ride-sharing app. Which of the following best combines requirements and use cases for the feature "Request a ride"?

hard

A. Requirement: The system must match riders with drivers within 2 minutes. Use case: Rider opens app, enters destination, and confirms ride request.

B. Requirement: The app must have a blue color theme. Use case: Driver updates profile picture.

C. Requirement: The system stores all ride data for 1 year. Use case: Admin views system logs.

D. Requirement: The app sends promotional emails weekly. Use case: Rider rates driver after ride.

Solution

1. Step 1: Identify relevant requirement for ride request

   Matching riders with drivers quickly is a key system requirement for this feature.

2. Step 2: Identify matching use case

   The use case describes the rider's interaction to request a ride step-by-step.

3. Step 3: Verify other options

   Other options mix unrelated requirements or use cases not tied to "Request a ride" feature.

4. Final Answer:

   Requirement: The system must match riders with drivers within 2 minutes. Use case: Rider opens app, enters destination, and confirms ride request. -> Option A

5. Quick Check:

   Requirement + user steps = correct combination [OK]

Hint: Match system needs with user steps for correct design [OK]

Common Mistakes:

• Mixing unrelated requirements and use cases
• Ignoring user interaction details
• Choosing cosmetic or admin features instead of core ones