Core Principles of Software Development

The Foundation Behind Modern Software Development Concepts like SOLID, DRY, KISS, YAGNI, TDD, DDD, etc...

💻 Recently, I conducted a couple of mock interviews for software engineering internships with university students. Many were focused on theoretical concepts and acronyms rather than understanding the underlying principles in simple terms.

I believe that all these concepts are derived from fundamental building blocks that we used decades ago and they are still valid and it is mandatory to understand by each software engineering individual.

1. Loose Coupling — If classes depend heavily on each other, they are tightly coupled. The less they rely on each other, the easier it is to modify them.
   👉 Example: A car radio can be replaced without impacting the entire car’s functionality.
2. High Cohesion — The degree to which elements of a whole belong together. Components should be highly cohesive to ensure they focus on a specific task.
   👉 Example: A class handling user login should not also handle payment processing.
3. Locality — Changes, maintenance, and extensions should be isolated, making it easy to manage without disrupting the entire system.
   👉 Example: Adding a new feature to your user profile section without needing to modify the rest of the app.
4. Removable — Software components should be easily removable without breaking the system.
   👉 Example: Removing an outdated payment gateway integration without affecting the checkout process.
5. Small Components — A software system should consist of small, focused components ideally doing only one task.
   👉 Example: A function that solely calculates tax, instead of calculating tax and shipping costs together.

🔄 Modern Concepts Derived from These Principles

SOLID Belongs to — Loose Coupling and High Cohesion

• A set of five design principles for writing maintainable and scalable code.
• Encourages flexible systems by reducing dependencies between components and ensuring that each component is focused on a single responsibility.

DRY (“Don’t Repeat Yourself”) — Belongs to — Locality and High Cohesion

• A principle that reduces redundancy in code, ensuring that information is centralized and reusable.
• Promotes maintainability by making sure that changes are made in one place and reflected across the system.

KISS (“Keep It Simple, Stupid”) — Belongs to Small Components and Locality

• A design principle encouraging simplicity and avoiding unnecessary complexity in software solutions.
• Encourages developers to break down tasks into smaller, manageable components.

YAGNI (“You Aren’t Gonna Need It”) — Belongs to — Removable and Small Components

• Reminds developers not to implement features until they are necessary, avoiding premature optimization.
• Keeps the codebase lean and avoids unnecessary complexity.

TDD (Test-Driven Development) — Belongs to High Cohesion and Loose Coupling

• A development practice where tests are written before the code, ensuring that the design meets the requirements.
• Ensures that each component is tested in isolation and works independently, improving reliability.

DDD (Domain-Driven Design) — Belongs to High Cohesion and Loose Coupling

• A design approach where the software architecture is modeled around the core business domain.
• Ensures that the structure of the software aligns closely with business objectives, leading to more understandable and maintainable systems that evolve as the business grows.

All these principles and concepts help developers create systems that are scalable, maintainable, and easy to change.

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