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4 April 2008

On the Requirements Heirarchy

Twice in the last month I have posted on “The 3 levels of requirements” (here and here).

The topic has also come up in a discussion thread at Modern Analyst which explores what the difference between functional specifications and business requirements specications is. (here)

The three levels are typically called;

Business requirements
Functional requirements
System requirements

Complementing functional requirements there are non-functional requirements. As a result, in some circles the functional requirements are called user requirements. To me this is a neat label because it keeps the focus on users and is a good term for addressing non-technical solutions.

So we can look at the hierarchy as;

Business requirements
User requirements
  • Functional requirements
  • Non functional requirements
  • And the non technical requirements
    System requirements

    To try to explain the relationship of these hierarchies I have put together a Venn diagram. I am interested in your comments, either here on in the Modern Analyst forum thread.

    And after posting the diagram above I realise I have not labelled the "User requirements" - but I don't have time to redo the picture; so be aware it's the second level.