High Level Design Document vs Low Level Design Document

sudhir_gs1
sudhir_gs1 used Ask the Experts™
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What are the contents of High Level Design Document and  Low Level Design Document ? How to start the Design Document? I would like to know for .Net with MS SQL Server and IIS. Please explain in detail .
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Senior Software Engineer
Commented:
Hi,

At this point you should have your requirements or most of them in a state that you know what you are going to build even though some of them might change during the development stage (if you are using an Agile methodology).

In UML you might use Use Case and Activity diagrams to show requirements.

In my opinion the High Level Design should show the system at a higher level of abstraction.
Basically what you are trying to show is HOW the system will be built, seperation of business tier, data tier and presentation tier.
You would show the classes (objects) that are needed to build each tier of the system and high level Entity Relationship Diagrams (ERD) or simply a listing of table names.

In UML you might use Class diagrams and Activity diagrams, Deployment diagrams, Package diagrams and Component diagrams to show HLD

The Low Level Deisgn should take the HLD to a lower level of abstraction where by the details of the classes and entitys are "Filled in". This shows in greater detail HOW the system will be built and will include all classes, fields, methods and signatures, interactions etc...

In UML you might use Interaction Diagrams (Sequence Diagrams) to show communication between objects in the LLD.

I know that I have used UML examples but you could simply create a document with class names for HLD and then with fields and methods for LLD.

Hope this helps,

Darren
DarrenSenior Software Engineer

Commented:
Hi,

Here are some links to other discussions you may have seen:

http://www.coderanch.com/t/99762/OO-Patterns-UML-Refactoring/Diffrence-between-High-Level-Desgin
http://www.linkedin.com/answers/technology/enterprise-software/TCH_ENT/171550-14949117

Template:
http://www.cmcrossroads.com/bradapp/docs/sdd.html

Just type 'high level design template' into Google and you will get plenty of hits, same for low level.

Cheers,

Darren

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Commented:
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