🧑‍💻 Author: RK ROY

📋 Real-World Case Studies

This section contains comprehensive case studies that demonstrate how to apply Low-Level Design principles and patterns to solve real-world problems. Each case study includes requirements analysis, design decisions, implementation, and explanations of the patterns used.

🎯 What You'll Learn

• How to approach system design from requirements to implementation
• When and how to apply design patterns in practice
• How different patterns work together in real systems
• Trade-offs in design decisions
• Best practices for maintainable, scalable code

📚 Available Case Studies

🅿️ 1. Parking Lot System

Complexity: Beginner to Intermediate
Patterns Used: Factory Method, Strategy, State, Observer
Concepts: OOP fundamentals, state management, payment processing

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What you'll learn:

• Vehicle type hierarchy design
• Parking spot allocation strategies
• Payment processing systems
• State management for parking spots
• Event-driven notifications

🏢 2. Elevator System

Complexity: Intermediate to Advanced
Patterns Used: State, Command, Observer, Strategy
Concepts: State machines, concurrent processing, scheduling algorithms

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What you'll learn:

• Complex state machine design
• Command queuing and processing
• Scheduling algorithms (FCFS, SCAN, LOOK)
• Thread-safe operations
• Real-time system considerations

💬 3. Chat Application

Complexity: Intermediate
Patterns Used: Observer, Command, Mediator, Factory
Concepts: Real-time messaging, user management, message routing

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What you'll learn:

• Message routing and delivery
• User presence management
• Group chat functionality
• Message persistence
• Real-time updates

📚 4. Library Management System

Complexity: Beginner to Intermediate
Patterns Used: Repository, Factory, Template Method, Strategy
Concepts: CRUD operations, data modeling, business rules

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What you'll learn:

• Book and member management
• Borrowing and return workflows
• Fine calculation strategies
• Search and filtering capabilities
• Data persistence patterns

🛒 5. E-commerce System

Complexity: Advanced
Patterns Used: Strategy, Decorator, Observer, Factory, Command
Concepts: Complex business logic, payment processing, inventory management

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What you'll learn:

• Product catalog management
• Shopping cart functionality
• Multiple payment methods
• Order processing pipeline
• Inventory tracking
• Discount and promotion systems

📱 6. Social Media Feed

Complexity: Advanced
Patterns Used: Observer, Strategy, Decorator, Composite
Concepts: Feed algorithms, content filtering, user interactions

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What you'll learn:

• Feed generation algorithms
• Content filtering and ranking
• User interaction tracking
• Privacy and security considerations
• Performance optimization techniques

🎮 7. Online Gaming System

Complexity: Expert
Patterns Used: State, Command, Observer, Flyweight, Prototype
Concepts: Real-time systems, performance optimization, scalability

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What you'll learn:

• Game state management
• Player action processing
• Real-time multiplayer considerations
• Performance optimization
• Scalability patterns

🎯 Learning Path Recommendations

🔰 For Beginners

Start with these case studies to build foundational understanding:

1. Library Management System - Basic CRUD operations and business logic
2. Parking Lot System - State management and simple patterns
3. Chat Application - Event-driven architecture basics

🚀 For Intermediate Developers

Build upon fundamentals with more complex scenarios:

1. Elevator System - Complex state machines and concurrency
2. E-commerce System - Advanced business logic and multiple patterns
3. Social Media Feed - Performance and scalability considerations

🏆 For Advanced Practitioners

Tackle the most complex scenarios:

1. Online Gaming System - Real-time systems and optimization
2. E-commerce System (advanced features) - Distributed systems concepts
3. Social Media Feed (scalability focus) - High-performance architectures

📊 Case Study Comparison

Case Study	Complexity	Patterns Count	Key Learning
Library Management	⭐⭐	4	CRUD, Basic Business Logic
Parking Lot	⭐⭐	5	State Management, Payment Processing
Chat Application	⭐⭐⭐	6	Real-time Communication, Event Handling
Elevator System	⭐⭐⭐⭐	7	Complex State Machines, Concurrency
E-commerce	⭐⭐⭐⭐	8	Advanced Business Logic, Multiple Integrations
Social Media Feed	⭐⭐⭐⭐⭐	6	Performance Optimization, Scalability
Gaming System	⭐⭐⭐⭐⭐	9	Real-time Systems, High Performance

🛠️ How to Use These Case Studies

1. Understand Requirements

• Read the problem statement carefully
• Identify functional and non-functional requirements
• Note any constraints or assumptions

2. Analyze the Solution

• Study the class diagrams and relationships
• Understand the design decisions made
• Identify the patterns used and why

3. Examine the Code

• Look at the implementation details
• Understand how patterns are implemented in code
• Note the trade-offs and alternatives

4. Practice and Extend

• Implement the solution yourself
• Add new features or modify existing ones
• Try different approaches or patterns

5. Review and Reflect

• Compare your solution with the provided one
• Identify areas for improvement
• Document lessons learned

🎨 Design Patterns Usage Across Case Studies

🔗 Cross-Case Study Concepts

Common Design Elements

1. User Management: Present in most systems
2. State Management: Critical for dynamic systems
3. Event Handling: Essential for responsive systems
4. Data Persistence: Required for most applications
5. Validation and Error Handling: Universal concerns

Reusable Components

Many components can be reused across different case studies:

• Authentication and authorization systems
• Notification services
• Payment processing modules
• Logging and monitoring systems
• Configuration management

📚 Additional Resources

Books

• "System Design Interview" by Alex Xu
• "Designing Data-Intensive Applications" by Martin Kleppmann
• "Clean Architecture" by Robert C. Martin

Online Resources

• High Scalability case studies
• Engineering blogs from major tech companies
• Open source project architectures

🎓 Assessment and Practice

Self-Assessment Questions

For each case study, ask yourself:

1. Understanding: Can I explain the system architecture without looking at the solution?
2. Application: Can I identify which patterns are used and why?
3. Extension: Can I add new features using the same design principles?
4. Alternatives: Can I suggest different approaches or improvements?

Practice Exercises

1. Modify Existing Systems: Add new features to the provided case studies
2. Combine Systems: Create a system that combines elements from multiple case studies
3. Scale Up: Design how you would handle increased load or users
4. New Case Studies: Create your own case study for a domain you're familiar with

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🚀 Getting Started

Ready to dive into real-world system design? Start with the Parking Lot System for a gentle introduction, or jump to any case study that interests you most!

Remember: The goal is not just to understand the solution, but to learn the thinking process behind good system design.

Happy Designing! 🎉

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