Now that the project manager and the client have agreed on the requirements (Requirements Specification), it is time to define how the project is going to be carried out.

This is the Design phase of the project.

In this phase the exact details are defined, for example :-

This is all about the nitty-gritty detail.  Once again this phase is trying to define the system in ever greater detail.

Think of the advantages of this phase - if you were the software engineer which would you rather have given to you as a job on a Monday morning?:-

Useless specification ! :-

a) Create a big file on the hard disk that will store all the invoices.

or

Useful, specific details...

b) The invoice file shall include a data record consisting of:-

1. Customer ID (3 digit alpha code)

2. Invoice number (9 digit number)

3. Value of item (displayed as currency)

4. .... yet more detail....

If you were the poor engineer given specification (a) the chances are you would not know where to start as you are bound to get it wrong!

So the design phase is really useful for the IT programmers who have to create the system.

Another aspect of creating a system is how are you going to test it?

It is tempting to leave the testing considerations until after the system has been developed but for the people having to develop the system it is really useful to have a test procedure in place before even starting to write a line of code or to design the hardware.

This is because you know how it will be tested and so it guides you towards a good design.

Example:

The input form shall reject

- any number greater than 1000

- any number less than zero

- any text

The input form shall accept

- any customer id and password the database already recognises

- shall jump to a 'new customer' screen (see details *** ) if it does not recognise the customer id.

Can you see why having this detail in the design phase would be useful to the project team?

Prototyping

A 'prototype' is something that represents what you will finally create without having to worry about all the details - it captures the essential details to confirm that the design is likely to work.

 In software, the prototype is often written in a kind of shorthand English 'Read in the record'.  The details do not matter at this stage, but a record must be 'read in'.

In hardware, you can test the system on a much cheaper slow computer, knowing that you will be able to run much faster on the final design - but it proves that the system works in principle.

The master document that is created in this phase is the 'Systems Requirement Document'

In a way, this is the contract between the project managers and the development team.