What is a High Level Design (HLD) ?

• HLD is a document and set of UML artifacts that defines the higher level component view of the system.
• It usually includes a high-level architecture diagram including the components, interfaces and networks.
• Mentions every work area briefly and clearly delegating the ownership of more detailed design activity to the concerned LLDs.
• May define high level domain model and interaction diagram which shall be elaborated in LLDs.
• Defines boundaries of the system, possible subsystems and establish communication methodologies within various sub-systems.
• HLD contains details at macro level and so it cannot be given to programmers as a document for coding.
• HLD may contain decisions stating the reason for the design decision. For example using Struts2 framework over Spring MVC.
• HLD is used by designers or senior developers to create LLDs for their subsystems strictly following the boundaries, interfaces and guidelines provided in HLD.