Low-Level Design for MAANG Interviews

A book-shaped table of contents for LLD interview prep: OOP fundamentals through SOLID, design principles, UML, design patterns, dependency management, reliability, concurrency, domain modeling, API design, testing, refactoring, classic interview problems, advanced architecture, and performance — cross-linking Object-Oriented Programming and Patterns instead of duplicating them.

1 — Identifying Entities

Covers how to identify entities in a domain model — objects with a persistent identity that spans changes to their attributes over time.

3 — Aggregates

Explains aggregates as consistency boundaries that group entities and value objects behind a single root for transactional integrity.

4 — Domain Services

Covers domain services for modeling operations that don't naturally belong to any single entity or value object in the model.

5 — Repositories

Introduces the repository pattern for abstracting aggregate persistence and retrieval behind a collection-like interface.