Requirements and use cases in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are requirements in system design?

Requirements are clear statements about what a system should do or the qualities it must have. They guide the design and development process.

beginner

Define use case in the context of system design.

A use case describes how a user interacts with a system to achieve a specific goal. It shows the steps and conditions involved.

intermediate

Why is it important to gather requirements before designing a system?

Gathering requirements helps ensure the system meets user needs, avoids costly changes later, and provides a clear direction for design.

intermediate

What is the difference between functional and non-functional requirements?

Functional requirements describe what the system should do (features), while non-functional requirements describe how the system performs (speed, security, usability).

intermediate

How do use cases help in validating system requirements?

Use cases provide concrete scenarios that show how users will interact with the system, helping to check if requirements cover real user needs.

What is the main purpose of a use case?

A To describe user interactions with the system

B To list hardware requirements

C To define database schema

D To write code modules

Use cases focus on how users interact with the system to achieve goals.

Which of the following is a non-functional requirement?

A The system must allow users to log in

B The system should respond within 2 seconds

C Users can upload files

D The system supports password reset

Response time is a performance-related, non-functional requirement.

Why are requirements important before system design?

A They help avoid misunderstandings and guide development

B They replace testing

C They are only needed after coding

D They define the programming language

Requirements clarify what the system should do and prevent costly mistakes.

Which statement best describes a use case?

A A list of hardware components

B A detailed technical specification

C A user story describing system interaction

D A database table design

Use cases describe user stories and interactions with the system.

Functional requirements specify:

A Hardware specifications

B System speed and security

C User interface colors

D System features and behaviors

Functional requirements define what the system should do.

Explain the difference between functional and non-functional requirements with examples.

Think about what the system does versus how well it does it.

Describe how use cases help in understanding and validating system requirements.

Consider how stories about users guide design.

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