Difference Between HLD and LLD
The main difference between HLD and LLD is the level of abstraction and detail involved in the system design process. High-Level Design (HLD) focuses on a system's overall architecture and top-level components. It is done during the early stages of the software development lifecycle (SDLC), often as part of the system analysis and design phase.
Low-Level Design (LLD) focuses on the detailed design of individual components or modules within the system. It is performed during the later stages of the SDLC after the HLD has been established.
Table of Contents (TOC)
Difference Between HLD and LLD
For better clarity, here's a tabular comparison between these two.
| Benchmark | High-Level Design (HLD) | Low-Level Design (LLD) |
|---|---|---|
| Abstraction Level | High-level, conceptual | Low-level, implementation-specific |
| Scope | Defines the overall system architecture, major components, and their interactions | Specifies the internal design and implementation details of individual components |
| Focus | Identifies the system's functional and non-functional requirements | Determines the algorithms, data structures, and programming constructs to meet the requirements |
| Perspective | Provides a bird's-eye view of the system | Delves into the granular details of each system component |
| Purpose | Establishes the foundation for the system's overall structure and behavior | Guides the actual coding and development of individual system components |
| Audience | Stakeholders, project managers, system architects | Developers, quality assurance team, maintenance engineers |
| Deliverables | System context diagram, use case diagrams, module decomposition, data flow diagrams | Class diagrams, sequence diagrams, activity diagrams, pseudocode, detailed API specifications |
| Timing | Performed early in the development lifecycle, often during the analysis and design phase | Conducted during the design and implementation phases, after the HLD is established |
| Level of Detail | High-level, conceptual descriptions | Granular, implementation-specific details |
| Changes | Changes at the HLD level can have a significant impact on the overall system | Changes at the LLD level are typically less disruptive and more localized |
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What is HLD?
A High-Level Design (HLD) is a preliminary design that outlines the structure and layout of a system or application. It describes the system's main components, how they interact with each other, and how data flows between them. HLD provides an overview of the system's architecture and functionality and serves as a starting point (blueprint) for the detailed design phase.
What is LLD?
Low-Level Design is the second stage of the software design process that comes after the HLD. LLD provides a detailed blueprint of the software system's architecture, including its components, modules, interfaces, and data storage.
This design phase is critical as it helps software developers to write efficient, scalable, and maintainable code. LLD typically involves creating flowcharts, data flow diagrams, pseudo-codes, and other technical documentation that helps to implement the software system's functionality.
Key Difference Between HLD and LLD
Here are the key differences:
- HLD focuses on the overall system architecture and top-level components, whereas LLD focuses on the detailed design of individual system components.
- HLD defines the major functional and non-functional requirements, but LLD specifies the internal structure, algorithms, and data structures.
- High-Level Design specifies system modules, their interactions, and data flow. In contrast, Low-Level Design delves into implementation-specific details and technologies.
- HLD provides a high-level, abstract view of the system, whereas LLD provides a granular, technical view.
- HLD is performed during the early stages of the development lifecycle, but LLD is performed later.
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