When building a robust application, there's a clear hierarchical flow from abstract concepts to concrete implementations.
This hierarchy ensures systematic development where each level builds upon and refines the previous one.

Software Architecture Guide

Here's the complete hierarchy for building robust applications:

1. Requirements Analysis & Business Context

Purpose: Understanding what needs to be built
Focus: Functional and non-functional requirements, business goals, user stories
Output: Requirements specification, use cases, acceptance criteria
Stakeholders: Business analysts, product managers, stakeholders

2. Software Architecture (Highest Level)

Purpose: Defines the fundamental organizational structure of the software
Focus: Architectural patterns, technology stack selection, foundational principles
Output: Architectural blueprint, technology choices (e.g., microservices vs monolith)
Stakeholders: Enterprise architects, principal engineers
Key Decisions: Microservices, Event-Driven, Layered Architecture, Serverless

3. System Design (Broad Implementation Planning)

Purpose: Translates architecture into a deployable system plan
Focus: Infrastructure, scalability, reliability, performance, security
Output: System architecture diagrams, infrastructure plans, deployment strategies
Stakeholders: System architects, DevOps engineers, infrastructure architects
Key Components: Load balancers, databases, caching layers, message queues, monitoring

4. High-Level Design (HLD) - System Architecture Detail

Purpose: Defines the overall system structure and major components
Focus: Component interactions, data flow, service boundaries, APIs
Output: System diagrams, component specifications, interface definitions
Stakeholders: Solution architects, tech leads, senior engineers
Key Elements: Major modules, service interactions, data models, external integrations

5. Low-Level Design (LLD) - Component Implementation Detail

Purpose: Detailed design of individual components and modules
Focus: Class design, algorithms, data structures, method specifications
Output: Class diagrams, sequence diagrams, detailed specifications, pseudocode
Stakeholders: Senior developers, tech leads, development teams
Key Elements: Object-oriented design, SOLID principles, interface definitions

6. Design Patterns (Implementation Solutions)

Purpose: Proven solutions to common design problems at the code level
Focus: Reusable design templates, best practices, code organization
Output: Pattern implementations, code templates, design guidelines
Application Level: Applied within LLD for specific implementation challenges
Categories: Creational, Structural, Behavioral patterns

The Flow in Practice

When building a robust application, the process flows systematically:

Phase 1: Strategic Planning

• Requirements Analysis → Software Architecture: Business needs drive architectural decisions

Phase 2: System Planning

• Software Architecture → System Design: Architectural patterns guide infrastructure choices

Phase 3: Detailed Design

• System Design → HLD: Infrastructure requirements shape component design
• HLD → LLD: Component specifications drive detailed implementation design

Phase 4: Implementation

• LLD → Design Patterns: Detailed designs use patterns for specific solutions

Relationship and Dependencies

Level	Depends On	Influences	Key Question
Requirements	Business needs	All design decisions	"What should the system do?"
Software Architecture	Requirements	System Design approach	"How should we structure the software?"
System Design	Software Architecture	Infrastructure and deployment	"How do we build and run this architecture?"
HLD	System Design	Component boundaries	"What are the major parts and how do they connect?"
LLD	HLD	Code structure	"How is each component implemented internally?"
Design Patterns	LLD challenges	Code quality and maintainability	"How do we solve this specific design problem?"

Prerequisites for Each Level

For HLD: Basic coding skills, understanding of databases, networking, microservices concepts, load balancing, message queues

For LLD: Object-oriented programming, design patterns, data structures and algorithms, SOLID principles

For Design Patterns: Strong OOP knowledge, understanding of common software problems, code refactoring experience

This hierarchical approach ensures that each level provides the foundation for the next, creating a systematic path from business requirements to maintainable code. Without proper execution at each level, the robustness of the final application is compromised.