Design Documents in Programming Methodology

In this tutorial you will learn about Design Documents in Programming Methodology, What is actually a design document, Kinds of design documents – High Level Design Document, Low Level Design Document and Uses of Design Document

What is actually a design document!

The design document gets developed by designer’s who design this in order to
give description of the product which the developers in the software development team use to develop the product. In short the design document gives in a nutshell the main idea and structure of the product that would be developed by developers.

The design document comes following the design of architecture diagram. This is the diagram which explains the architecture which would be used for developing the software product. The architecture diagram contains one or more of the following namely the technology that would be used to develop the software product, description of the product that would be developed, description of the interfaces that would be used in the development process for communication, the main components that would be developed for the product, the interfaces that would be developed between different components, the hardware requirement for developing the software product and so on. The above all would be analyzed and designed in architecture diagram. Following this architecture diagram design the design of design document phase starts.

Kinds of design documents:

The design document is mainly classified as two types namely

High Level Design Document also called as HLD
Low Level Design Document also called as LLD

High Level Design Document:

High Level Design Document is the acronym for HLD. The high level design
document must be designed by taking into account one or more of the following namely

• Careful analysis and study of requirement document must be made to prepare the design document. This is because it is vital that all the items addressed in requirements document must be brought under design document.
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• High level deign gives the overview of the development of product. In other words how the program is going to be divided into functions, modules, subdivision etc.
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• The design document prepared must be prepared taking into account things like how to develop the product in other words say for instance how the program is going to be divided into functions, modules, subdivision etc. so that they are easily maintainable in later stage.
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• Design document must be designed also taking into account things like easy portability of the software product to different systems

Low Level Design Document:

Low Level Design Document is the acronym for LLD. The Low Level Design Document gives the design of the actual program code which is designed based on the High Level Design Document. A good Low Level Design Document developed will make the program very easy to be developed by developers because if proper analysis is made and the Low Level Design Document is prepared then the code can be developed by developers directly from Low Level Design Document with minimal effort of debugging and testing.

In general the design document designed have the following namely

• The design document starts by giving a description about the purpose of the design document
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• Has sections in design document which explain what all area would be covered in the design document in others words has description about scope of the design document
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• The design document has sections which gives explanations about the
  …………Document which was used as input for this document for instance
  …………one could be say user requirements document and so on
  
  …………Document which would be resulted as output from the design
  …………document for instance say a test plan and so on
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• Design document has an abstract section. This section gives a summary about the design document designed.
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• Design document has a diagram showing the system architecture
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• Design document also has details about functions of the software product.

Apart from the above contents present in design document varies depending upon the type of design document as explained above.

Uses of Design Document

A Good design document so analyzed and prepared helps in the following ways

• Good design document helps the development team to give quality product
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• Design document analyses the timeline for each component development. So over all rough estimated time of completion can be calculated in the design documents stage itself. This can be used to compare with the target date set for completion of the project. If the time is greater than target date then unwanted and less important components can be left and may be taken off for next phase of development. Thus the design documents helps to divide the development stage into several phases and set target dates for each to achieve the total product delivered to customer on time. Thus on whole good design document helps to deliver quality software product within the timeframe.

• A good design document for instance a good low level deign document prepared will be very helpful to the developers in developing team. This is because the low level design document has the program code and if the low level design document prepared is very good programmers or developers need not spend much time in error correction and hence time for development gets reduced and thus productivity is increased. Also good low level design document gets prepared only if the high level design document from which it is prepared is good.

So it is very essential to have a good design document for a software product to be developed on time with good quality.