Preliminary Requirements


Identify Functional Requirements

The purpose is to gather just enough of the functional requirements to understand if a potential solution will be suitable.
  • High Level Scope
    1. Carry out a workshop to determine functional requirements at level 1 and 2
  • Functional decomposition to level 2

The hardest part of this exercise is keeping at a high level. People will want to drill down to specify minor details such as the ability to select a salutation from a list and customise the order of the list to suit each business user. What you really want to record is that you need the ability to capture and manage names and probably addresses. In terms of a functional decomposition, level 1 would be 'Client Details' and a level 2 item may be "Manage Client Details". If you did get down to customised lists it would probably be level 4. Level 3 would be 'Manage Client Name' and Level 4 would be 'Customise Salutations".

If in doubt whether you are drilling down too far, ask yourself

"In order to get an understanding of whether a package is likely to be suitable, do I need to know this information? Would I reject the solution if this feature was not present?"

If your organisation is more familiar with other techniques such as Use Cases or Data Flow Diagrams, you can use this approach but the same rules apply.

Only go down to the level you need. If people want to go down further, explain that no package will exactly fit their requirements. It is likely that the selected package will have features they have not thought of, or do things in a slightly different manner. They should expect that some existing business processes will need to change. Defining an ideal may be a waste of time if it cannot be achieved in the selected package, or if the package accomplishes the same outcome in a different way.

During the process also note if a function is mandatory or optional. Would the lack of a particular function be a deal breaker if it could not be delivered? In reality, you may select a package and customise it to deliver a function that it did not have, but it does get the thinking going around what is absolutely necessary.

As part of this activity, it is likely that data entities will be identified. These should be noted down and used in the next activity which looks at data.

Functional Decomposition Worksheet An Excel Worksheet with a number of macros to assist in the capture of functional requirements. Worksheet can be used with a data projector in a workshop situation.
Functional Decomposition User Guide Description of a functional decomposition including an example. Instructions for carrying out a functional decomposition.

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