HLd

HLD is an acronym that can refer to more than one concept in technology and computer science, depending on the context. Two of the most common meanings are High-Level Design in software engineering and Heavy-Light Decomposition in algorithm design. Both usages appear in documentation and discussions about systems, but they address different problems: one concerns architectural planning, the other concerns efficient query processing on tree data structures.

High-Level Design (HLD) is the phase in software development that translates requirements into an overall system architecture and component plan. It focuses on the major modules, their interfaces, data flows, and how the system meets nonfunctional requirements such as scalability, reliability, and security. HLD typically precedes Low-Level Design and detailed implementation, and it serves as a bridge between business analysts, architects, and developers. Common deliverables include architectural diagrams, technology choices, data models at a coarse level, and a mapping from requirements to components.

Heavy-Light Decomposition is a technique used in data structures to answer queries on trees efficiently. The idea is to partition a rooted tree into disjoint heavy paths, where each node selects a heavy child with the largest subtree. This creates a set of heavy paths that cover every edge, enabling path queries and updates to be broken into a small number of path segments. When combined with a segment tree or Fenwick tree on each path, operations such as path sum, path maximum, or subtree queries can be performed in logarithmic time.

Users should determine the intended meaning from context, as HLD may refer to design practices or to algorithmic methods.