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Low-level design

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Low Level Design (LLD) is a component level design process that follows up a step by step process of refinement which may be used for the design of data. Overall the data organization may be defined during requirement analysis, refined during data design work, and then each component is specified in detail.[1]

The low-level design (LLD) phase the stage where the actual software components are designed.

During the detailed phase the logical and functional design is done and design of application structure is developed during the high level design phase.

Design phase

A Design is a structure of system and it interactes with the other systems. A good design is important to achieve high reliability, low cost and good maintainability.[2] We can distinguish two type of program design phase.

1) Architectural or high-Level design

2) Detailed or Low-level design

Structured flow charts and HIPO diagrams typify the class of software design tools and these provide a high-level overview of a program. The advantages of such a design tool are that it yields a design specification which is understandable to non programmers and it provides a good pictorial display of module dependencies. The disadvantages is it may be difficult for software developers to go from graphic oriented representation of software design to the actual implementation of the software system. Therefore, it is necessary to yield little insight into the algorithmic structure describing procedural steps, to facilitate the early stages of software development.(generally using PDLs)[3]

Purpose

The goal of Low Level Design (LLD)|Low Level Design Document(LLD) is to give the internal logical design, of the actual program code. High Level Design is created on the Low level design. LLD describes the class diagrams with all the methods, relation between classes and programs specs. It describes each and every module in an elaborate manner so that the programmer can directly code the program from the document.

A good Low Level Design Document will make the program easy to be developed when proper analysis is made to create Low Level Design Document. The code can then be developed directly from Low Level Design Document with minimal effort of debugging and testing. It also adds other advantages such as lower cost and easier maintainability of Project.

Sample

An example is provided of HLD:Sample HLD, after iterations which is developed as LLD  :Sample LLD

References

  1. ^ Software Engineering: A Practitioner’s Approach Roger S. Pressman
  2. ^ The Essence of Program Design: By Bell Stephen P., Douglas Bell, Ian Morrey, John Pugh
  3. ^ Survey of Program Design Languages (PDLs): Brian A. Nejmeh, Herbert E. Dunsmore