The design phase can be described as “working out how we are going to do it”. The analysis phase resulted in the data model and the specification of new requirements. This clearly describes what is required for the new product. Working out how to build the product poses a huge number of decisions such as:

• Which technology should be used?
• What architecture should be selected?
• What database architecture should be used?
• How should the user interface be designed?
• What are the performance requirements and how can they be achieved?

The preliminary stage of design is often a prototype of the user interface. This is quickly constructed to provide a tangible example of the developer’s interpretation of requirements.

Many small, fast iterations will be made to the prototype, allowing the client to correct design discrepancies. This approach has the added benefit that the user can check the system inputs and outputs at the earliest stage.

When the user is satisfied with the interface prototype, the job of designing the architecture of the application is undertaken.