License To Crack - Design Phase

High Level Design (HLD)

Based on the SRS, now the software systems analysts will take over to convert the requirements into a usable product. In order to achieve this, the systems analysts must design the application, which will help the programmers in coding. In the design process, the product is to be broken down in independent modules and then taking each module at a time and then further breaking them to arrive at micro levels. There are 2 different approaches followed in designing,

1) top-down approach and 2) bottom-up approach.

In top-down approach, the product is broken continuously into smaller levels till it cannot be broken to further levels. In bottom-up approach, the smaller levels and designed first and the used as building blocks to go to next higher level till we reach the complete product level.

The HLD document will contain the following items at a macro level. In HLD, the systems analyst describes what is to be done in the product. It will not go in depth into each component of the product.

-- List of modules and a brief description of each module.
-- Brief functionality of each module.
-- Interface relationships among modules
-- Dependencies between modules (if exists, B exists etc.)
-- Data elements that are used by customer
-- Overall architecture diagrams along with technology details.

This document is one step ahead SRS, to convert the requirement into a product. This is mostly a single document, for small to medium size projects. But if the application is large, then there may be multiple documents, which form the whole HLD. Each document may describe a separate module.

Low Level Design (LLD)

HLD contains details at a macro level and so it cannot be given to programmers as a document for coding. So, the systems analysts prepares micro level design document, called Low Level Design. This document describes each and every module in an elaborate manner, so that the programmer can directly code the program based on this. There will be at least one document for each module and there may be multiple LLDs for a module, depending upon the complexity of the module.

The LLD document will contain the following sections.

-- Detailed functional logic of the module, in pseudo code. -- Database tables, with all elements, including their type and size -- All interface details with complete API references ( requests and responses) -- All dependency issues between modules -- Error message Listings -- Complete UI design of how each screen looks like

The HLD and LLD phases put together is called Design phase. Design must be done only by experienced people. Design itself has its own guidelines to be followed; most of the times, people use design patterns to find out what will be the best design for a product. Already there are many experts in the world, who have designed big products; they had published the way they designed. Instead of reinventing the wheel, we can try to reuse those already proven designs, if they fit our software.