System Design Approach

Initial Planning Steps

Before designing a system, determine whether the focus is on:

• OOAD (Object-Oriented Analysis & Design)
  or
• Large-Scale System Architecture

This sets the scope for how deep you go into components, storage, APIs, and scaling.

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Core System Design Process

1. Clarify Requirements
   Understand product goals, user flows, business rules, constraints.

2. Define Data Storage
   Choose database types (SQL / NoSQL) and design schemas.

3. Define Services & APIs
   Map business logic to API endpoints, services, and system boundaries.

4. Plan for Scaling
   Design both application and database scaling strategies.

   • Determine expected load (QPS, daily active users)
   • Estimate instance requirements
   • Identify bottlenecks and limits early

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Documentation Framework

Product Requirements Document (PRD)

• Defines features, expected behavior, and constraints
• Acts as a business blueprint for engineering
• Example: eBay mobile app download banner
  • Where should the banner appear?
  • How often should it appear?
  • How will success be measured?

Technical Design Document (TDD)

• Contains all technical architecture decisions
• Includes:
  • Data storage and schemas
  • Services and APIs
  • Scaling strategy
  • Error handling & security considerations

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Software Development Life Cycle (SDLC)

SDLC provides a systematic process for building high-quality software while managing cost and time.

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Phase 1: Requirement Analysis

• Study Current System
  Assess workflows, identify inefficiencies, gather performance data.

• Identify User Requirements
  Interviews, surveys, shadowing, focus groups.

• Resource Planning
  Budgeting, team size, tooling requirements.

• Schedule Planning
  Milestones, timelines, cost estimations.

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Phase 2: Design

High-Level Design (HLD)

• Technology stack (e.g., Java, Python, Docker, MySQL)
• Architecture (Monolithic vs Microservices)

Low-Level Design (LLD)

• Business logic flows
• Database schema design
• Error handling strategy
• Security, authentication, and access control

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Phase 3: Implementation

• Backend Development
  Java, JavaScript, or chosen backend language

• Frontend Development
  Framework selection, component architecture, state management

• Best Practices
  Design patterns, SOLID principles, code documentation

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Phase 4: Testing

Functional Testing

• Unit tests
• Integration tests

Non-Functional Testing

• Performance
• Usability
• Security
• Compatibility across devices/browsers

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Phase 5: Deployment

Deployment Models

• On-Premises
  • Full ownership and control
  • Higher initial costs
• Cloud Deployment
  • AWS, Azure, GCP
  • Elasticity, flexibility, managed services

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Phase 6: Maintenance

• Bug fixes
• Feature enhancements
• Performance optimizations
• System monitoring and alerting

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SDLC Models

Waterfall Model

• Sequential and rigid
• Heavy documentation
• Minimal customer feedback
• Suitable for well-defined requirements

Agile Model (≈90% industry adoption)

• Iterative and flexible
• Continuous customer feedback
• Short development cycles
• Collaboration prioritized over documentation

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Agile Framework: Scrum

Core Components

Sprint Structure

• Time-boxed (commonly 2 weeks)
• Each sprint delivers a usable product increment

Scrum Roles

• Product Owner
  Owns product backlog and prioritization

• Scrum Master
  Facilitates process, removes blockers

• Development Team
  Developers, QA engineers, DevOps, UI/UX designers, architects

Scrum Events

• Sprint Planning
  Define sprint goals and tasks

• Daily Stand-ups
  Short updates and blocker identification

• Sprint Review
  Showcase completed work to stakeholders

• Sprint Retrospective
  Analyze what went well and what needs improvement

Scrum Artifacts

• Product Backlog — prioritized user stories
• Sprint Backlog — tasks for the current sprint
• Product Increment — completed, releasable work

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Development Environments

1. Local Environment — developer’s personal workspace
2. Development (Dev) — shared team integration environment
3. Quality Assurance (QA) — testing by QA team
4. User Acceptance Testing (UAT) — validated by end-users or clients
5. Staging — production-like environment for final validation
6. Production — live environment for end users

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Key Roles in Development

• Project Manager — timeline and resource management
• Product Manager — market research, PRD creation
• UI/UX Designer — interface and experience design
• System Architect — overall system blueprint
• Developers — frontend, backend, full-stack
• QA Engineer — test planning and validation
• DevOps Engineer — CI/CD and deployment automation

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Practical Application

From Theory to Practice

• Requirement Analysis
  PRD, user stories, prototyping

• Design
  Tech selection, TDD creation, architecture reviews

• Implementation
  Code development, unit testing

• Testing
  Ensure feature quality and reliability

• Deployment
  Move through environments → Production

• Maintenance
  Long-term support and iteration

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Success Measurement

• Define clear KPIs and metrics
• Establish data collection processes
• Use A/B testing or randomized sampling
• Create continuous feedback loops