High-level system design and low-level system design in software development

The software development cycle goes through many processes, High-Level System Design (HLSD) and Low-Level System Design (LLSD) are just two parts.

Software Development Life Cycle (SDLC) goes through multiple phases like planning, requirement assessment, analysis, design, execution, documentation, testing, etc. Each phase is further divided into tasks with properly defined goals and outcomes.

Analysis and design are the phases in which the actual architecture, working model, and execution procedures for building a software product are determined.

Two key steps in these phases are high-level system design and low-level system design.

What is Advanced System Design?

High-Level Design (HLD) provides a comprehensive overview of the software development process, as well as a complete flowchart of system architecture, applications, database management, and systems and navigation. It is a blueprint that integrates the various steps and modules of developing software, their goals, variable components, results, architecture, and timelines. HLD transforms business plans into software products or services.

Examples of HLDs in software development include system architecture documents, application development flow charts, etc.

What is Low-Level System Design?

Low-Level Design (LLD) deals with the planning, coding, and execution of the various components, modules, and steps in HLD at a single level. Each module in HLD has a unique LLD document that provides comprehensive details on how the module is coded, executed, quality tested, and integrated into the larger program. LLD provides an actionable plan by deconstructing HLD components into working solutions.

Examples of LLD in software development include shopping cart integration, security testing, user interface design, etc.

Difference between HLD and LLD

HLD and LLD also have different functions and uses, such as high-level programming language and low-level programming language.

Macro and Micro Architecture and Design

HLD is a macro design that provides a bird's eye view of the software development process. It includes diagrams, flow charts, navigation details, and other technical requirements that will form the crux of the development process.

In addition to flow charts, diagrams, navigation information and technical requirements, LLD also provides comprehensive information about the step-by-step execution of each component of HLD. It deals with software development at a micro level.

Each component of the HLD has a unique LLD document.

Development timeline

The HLD precedes the LLD stage. Once the HLD is in place and approved for execution, work on the individual LLDs can begin.

HLD begins after the planning and requirements phases are addressed and has no other dependencies.

On the other hand, LLD requires execution in a specific order. Some modules must wait to execute until other modules are completed.

LLD belongs to the design phase of SDLC, while HLD belongs to the analysis phase of SDLC.

Purpose

The purpose of the HLD is to list the functional aspects of the various modules and the end results.

The purpose of the LLD is to detail the logic and execution of each module in the HLD.

Stakeholders

The Solution Architect is responsible for creating the HLD document. It can have internal and external stakeholders such as the review team, design team, customers, and managers who are responsible for understanding the software metrics.

LLD is handled by software developers, web administrators, security engineers, etc. within a company or vendor team. LLD is usually limited to internal stakeholders.

Target Audience

The target audience for HLD documents are managers, customers, and software development teams.

Software engineers, coders, testers, and developers working on the project are the target audience for LLD documents.

Expected Results

The result of HLD is a software product or service that is ready for delivery to the end user.

The result of LLD is the completion of a single module of HLD, such as the coding or testing phase.

Understanding Software Design Documents

In addition to technical requirements and other implementation details, software design documents outline the structural, functional, and logical aspects of developing a software product or service. Whether the design deals with the macro level or the micro level of execution, programmers and other stakeholders should know and understand the scope and individual steps of the software development process.