High Level Design (HLD) and Low Level Design (LLD)

High Level Design (HLD): 

The HLD stands for High-Level Design, where the designer will only focus on the various models, like: 

• Decision Tables 
• Decision Trees 
• Flow Diagrams 
• Flow Charts 
• Data Dictionary 
• The solution architect develops the High-level design, which is used to specifies the complete description or architecture of the application. 
• The HLD involves system architecture, database design, a brief description of systems, services, platforms, and relationships among modules. 
• The HLD is also known as macro-level or system design. It changes the business or client requirement into a High-Level Solution. 
• The High-level design is created before the Low-Level Design.  

Low Level Design (LLD): 

• The LLD stands for Low-Level Design, in which the designer will focus on the components like a User interface (UI). 
• The Low-level design is created by the developer manager and designers. 
• It is also known as micro-level or detailed design. The LLD can change the High-Level Solution into a detailed solution. 
• The Low-level design specifics the detailed description of all modules, which implies that the LLD involves all the system component’s actual logic. It goes deep into each module’s specification. 
• The Low-level design is created after the High-Level Design. 

HLD vs LLD 
 

S.NO.	Comparison Basis	HLD	LLD
1.	Stands for	It stands for High-Level Design.	It stands for Low-Level Design.
2.	Definition	It is the general system design, which means it signifies the overall system design.	It is like describing high-level design, which means it signifies the procedure of the component-level design.
3.	Purpose	The HLD states the concise functionality of each component.	LLD states the particular efficient logic of the component.
4.	Also, known as	HLD is also called a System or macro-level design.	LLD is also called details or micro-level design.
5.	Developed by	Solution Architect prepares the High-Level Design.	Designer and developer prepare the Low-Level Design.
6.	Sequential order in the design phase	It is developed first in sequential order, which implies that the HLD is created before the LLD.	It is developed after High-level design.
7.	Target Audience	It is used by management, program, and solution teams.	It is used by designers, operation teams, and implementers.
8.	Conversion	The HLD changes the client or business requirement into a high-level solution.	The LLD changes the high-level solution to a comprehensive solution.
9.	Probable output	The high-level design is necessary to understand the flow across several system objects.	A low-level design is required for creating the configurations and troubleshooting inputs.
10.	Input Criteria	The input measure in high-level design is SRS (Software Requirement Specification).	The input measure in low-level design is the reviewed HLD (High- Level Design).
11.	Output Criteria	The output measures in the HLD are functional design, database design, and review record.	The output bases in the low-level design are the unit test plan and program specification.