High-Level Design (HLD) and Low-Level Design (LLD) are two crucial stages in the System Design Phase of the Software Development Life Cycle (SDLC). Both serve different purposes and are used at different stages of software development.
Key Differences Between HLD and LLD
| Feature | High-Level Design (HLD) | Low-Level Design (LLD) |
|---|---|---|
| Definition | Provides an overview of the system’s architecture, components, and interactions. | Provides detailed implementation-level design, including modules, classes, and data structures. |
| Scope | System-wide design; focuses on architecture, modules, and external dependencies. | Module-level design; focuses on internal components, functions, and logic. |
| Granularity | Abstract and broad. | Detailed and specific. |
| Focus Area | Defines system structure and relationships between components. | Defines how individual components or modules are implemented. |
| Used By | Architects, System Designers, Senior Developers. | Developers, Testers, Implementation Teams. |
| Output/Deliverables | Architectural diagrams, component diagrams, technology stack, data flow diagrams. | Class diagrams, sequence diagrams, database schemas, API specifications, function definitions. |
| Example | “The system will have authentication, a database, and an API.” | “The authentication module will validate user credentials using JWT tokens and store encrypted passwords in PostgreSQL.” |
| Tools Used | UML Diagrams, Visio, Lucidchart, Draw.io, Enterprise Architect. | UML Class Diagrams, ER Diagrams, API Documentation (Swagger), Database Design Tools. |
| Complexity | Focuses on how different parts of the system interact at a high level. | Focuses on internal logic, algorithms, and class-level details. |
| Changes & Modifications | Less frequent, as architecture changes affect the entire system. | More frequent, as code logic evolves during development. |
📌 Conclusion
- HLD gives a macro-level view of the system architecture.
- LLD provides detailed implementation logic at the module level.
- Both are essential for building a scalable, maintainable, and efficient system.
