Requirements and use cases in LLD - Architecture Diagram

System Overview - Requirements and use cases

This system captures and manages requirements and use cases for software projects. It helps teams collect, organize, and track what the software must do and how users will interact with it. Key needs include clear documentation, easy updates, and traceability between requirements and use cases.

Architecture Diagram

User
  |
  v
Web Client
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +-------------------+
  |                   |
  v                   v
Requirements Service  Use Case Service
  |                   |
  v                   v
Database             Database
  |
  v
Cache

Components

User

actor

Interacts with the system to create and view requirements and use cases

Web Client

frontend

User interface for managing requirements and use cases

Load Balancer

load_balancer

Distributes incoming requests evenly to backend services

API Gateway

api_gateway

Routes requests to appropriate backend services and handles authentication

Requirements Service

service

Manages requirement data including creation, updates, and retrieval

Use Case Service

service

Manages use case data and links them to requirements

Database

database

Stores persistent data for requirements and use cases

Cache

cache

Speeds up frequent read operations for requirements and use cases

Request Flow - 13 Hops

User → Web Client

Web Client → Load Balancer

Load Balancer → API Gateway

API Gateway → Requirements Service

Requirements Service → Cache

Cache → Requirements Service

Requirements Service → Database

Database → Requirements Service

Requirements Service → Cache

Requirements Service → API Gateway

API Gateway → Load Balancer

Load Balancer → Web Client

Web Client → User

Failure Scenario

Component Fails:Database

Impact:New writes fail and fresh reads cannot be served; cached reads still work but may be stale

Mitigation:Use database replication for failover; rely on cache for read availability; alert admins for repair

Architecture Quiz - 3 Questions

Which component routes user requests to the correct backend service?

A Load Balancer

B API Gateway

C Cache

D Database

Design Principle

This architecture separates concerns by using dedicated services for requirements and use cases, fronted by an API Gateway for routing and security. Caching improves read performance and reduces database load. Load balancing ensures even traffic distribution. The design supports scalability, fault tolerance, and clear data flow.

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