Requirements gathering (functional and non-functional) in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct functional requirement

Which of the following is a functional requirement for an online bookstore system?

A The system shall allow users to search for books by title, author, or ISBN.

B The system shall be available 99.9% of the time.

C The system shall respond to user requests within 2 seconds.

D The system shall encrypt user passwords using AES-256.

💡 Hint

Functional requirements describe what the system should do.

Option A describes a specific feature the system must provide, which is a functional requirement. Options A, B, and D describe qualities or constraints, which are non-functional requirements.

🧠 Conceptual

intermediate

Identify the non-functional requirement

Which of the following is a non-functional requirement for a mobile banking app?

A The app shall allow users to transfer money to other accounts.

B The app shall support fingerprint authentication for login.

C The app shall process transactions within 3 seconds.

D The app shall provide monthly account statements.

💡 Hint

Non-functional requirements describe how the system performs or behaves.

Option C specifies a performance constraint (processing time), which is a non-functional requirement. Options B, C, and D describe features or functions.

❓ tradeoff

advanced

Tradeoff between functional and non-functional requirements

A video streaming service wants to add a new feature to allow offline downloads (functional requirement). However, this feature may increase storage costs and affect app performance (non-functional concerns). What is the best approach to handle this tradeoff?

A Remove the feature to keep non-functional requirements intact.

B Analyze impact, optimize feature design, and balance both requirements.

C Delay the feature indefinitely until non-functional issues disappear.

D Ignore non-functional concerns and implement the feature fully.

💡 Hint

Good system design balances functional and non-functional needs.

Option B suggests analyzing and optimizing to balance both types of requirements, which is best practice. Options A and B are extreme and ignore important concerns. Option B delays progress unnecessarily.

❓ Architecture

advanced

Classify requirements for a ride-sharing app

Given these requirements for a ride-sharing app, classify each as functional (F) or non-functional (NF):
1. The app shall allow users to book rides.
2. The app shall encrypt user data.
3. The app shall handle 10,000 concurrent users.
4. The app shall provide driver ratings.

A 1-F, 2-NF, 3-NF, 4-F

B 1-F, 2-F, 3-NF, 4-NF

C 1-NF, 2-F, 3-F, 4-NF

D 1-NF, 2-NF, 3-F, 4-F

💡 Hint

Functional requirements describe features; non-functional describe qualities.

Booking rides and driver ratings are features (functional). Encrypting data and handling many users are qualities (non-functional).

❓ estimation

expert

Estimate capacity based on non-functional requirements

A new messaging app expects 1 million daily active users. The non-functional requirement states the system must handle peak loads with 10 messages per user per day, with 99.99% uptime. What is the minimum message processing capacity per second the system should support during peak hours (assuming peak hour is 10% of the day)?

A Approximately 1,000,000 messages per second

B Approximately 1,157,400 messages per second

C Approximately 11,574 messages per second

D Approximately 1,157 messages per second

💡 Hint

Calculate total messages per day, then divide by peak hour seconds.

Total messages = 1,000,000 users * 10 messages = 10,000,000 messages/day.
Peak hour = 10% of 24 hours = 2.4 hours = 8640 seconds.
Capacity = 10,000,000 / 8640 ≈ 1157 messages/sec.
Check options carefully; option D matches closest after unit conversion.

Practice

1. Which of the following best describes a functional requirement in system design?

easy

A. A usability guideline for user interface design

B. A quality that defines how fast the system should respond

C. A security measure to protect user data

D. A feature that defines what the system should do

Solution

1. Step 1: Understand functional requirements

   Functional requirements specify the actions or features the system must perform, such as user login or data processing.

2. Step 2: Differentiate from non-functional requirements

   Non-functional requirements describe qualities like speed, security, or usability, not specific features.

3. Final Answer:

   A feature that defines what the system should do -> Option D

4. Quick Check:

   Functional = What system does [OK]

Hint: Functional = what system does; Non-functional = how well [OK]

Common Mistakes:

• Confusing functional with non-functional requirements
• Thinking security is a functional requirement
• Mixing usability with system features

2. Which of the following is a correct example of a non-functional requirement?

easy

A. The system shall respond to user requests within 2 seconds

B. The system shall provide a search feature

C. The system shall store user profiles

D. The system shall allow users to reset their password

Solution

1. Step 1: Identify non-functional requirements

   Non-functional requirements describe system qualities like performance, reliability, or security.

2. Step 2: Match options to definitions

   The system shall respond to user requests within 2 seconds specifies response time, a performance metric, which is non-functional. Others describe features (functional).

3. Final Answer:

   The system shall respond to user requests within 2 seconds -> Option A

4. Quick Check:

   Non-functional = system qualities [OK]

Hint: Look for qualities like speed or security for non-functional [OK]

Common Mistakes:

• Choosing features as non-functional requirements
• Ignoring time or performance constraints
• Confusing functional and non-functional examples

3. Given these requirements:

• The system must allow users to upload files.
• Uploads must complete within 5 seconds.
• The system must support 1000 concurrent uploads.

Which of these is a functional requirement?

medium

A. Uploads must complete within 5 seconds

B. The system must support 1000 concurrent uploads

C. The system must allow users to upload files

D. The system must ensure uploaded files are available 99.9% of the time

Solution

1. Step 1: Identify functional requirements

   Functional requirements describe what the system does, such as allowing file uploads.

2. Step 2: Analyze each option

   A is performance (non-functional). B is capacity/scalability (non-functional). D is availability (non-functional).

3. Final Answer:

   The system must allow users to upload files -> Option C

4. Quick Check:

   Functional = system features [OK]

Hint: Features = functional; qualities like speed = non-functional [OK]

Common Mistakes:

• Selecting performance, capacity, or availability as functional
• Confusing capacity constraints as functional
• Ignoring direct feature statements

4. A system requirement states: "The system shall handle 1000 requests per second." Which type of requirement is this and what is wrong if it is listed as functional?

medium

A. Functional; it describes a feature, so it's correct

B. Non-functional; it describes performance, so listing as functional is incorrect

C. Functional; it describes user behavior, so it's correct

D. Non-functional; it describes security, so listing as functional is incorrect

Solution

1. Step 1: Identify requirement type

   Handling 1000 requests per second is about performance, a non-functional quality.

2. Step 2: Explain why listing as functional is wrong

   Functional requirements describe features, not performance metrics. Mislabeling causes confusion in design and testing.

3. Final Answer:

   Non-functional; it describes performance, so listing as functional is incorrect -> Option B

4. Quick Check:

   Performance = non-functional [OK]

Hint: Performance metrics are non-functional, not features [OK]

Common Mistakes:

• Calling performance a functional requirement
• Confusing user behavior with system qualities
• Ignoring the impact of mislabeling requirements

5. You are gathering requirements for a new messaging app. Which combination below correctly pairs functional and non-functional requirements?

hard

A. Users can send messages; messages must be delivered within 1 second

B. Messages must be encrypted; users can create profiles

C. The app must support dark mode; users can block contacts

D. The app must be available 24/7; Messages must be delivered with 99.99% reliability

Solution

1. Step 1: Identify functional requirements in options

   Functional requirements describe features like sending messages or creating profiles.

2. Step 2: Identify non-functional requirements in options

   Non-functional requirements describe qualities like speed, availability, or security.

3. Step 3: Analyze each option pair

   Users can send messages; messages must be delivered within 1 second pairs sending messages (functional) with delivery speed (non-functional). Others mix two functional or two non-functional requirements incorrectly.

4. Final Answer:

   Users can send messages; messages must be delivered within 1 second -> Option A

5. Quick Check:

   Functional + Non-functional = Users can send messages; messages must be delivered within 1 second [OK]

Hint: Functional = features; Non-functional = qualities like speed or availability [OK]

Common Mistakes:

• Mixing two functional or two non-functional requirements
• Confusing UI features with system qualities
• Ignoring delivery time as non-functional