A user of the program only interacts with a program through the user interface so it makes sense to spend a significant amount of time during requirements to ensure that the user interface makes sense, that all functionality is included, and that the most commonly used functionality is easily accessible. The easiest way of doing this is using a screen prototype. There are a variety of methods of making screen prototypes which range from simply drawing the interface with a pen and paper to building “working” prototypes in a higher level language like Visual Basic which allows rapid screen design. However, each of these extremes has serious drawbacks. A pen and paper prototype does not allow users to interact with the prototype and it is more difficult to change. A “working” prototype done in a programming language like Visual Basic can lead the client to believe that the program is nearly complete and that development should not take very long or it can lead the client to believe that changes to the prototype will be costly making them reluctant to make necessary suggestions to improve the program.
Between these two extremes lies screen design applications which allow you to draw the screens and model interactions between screens. High quality prototyping tools allow you to enter sample data and allow users to move between screens by pressing buttons so they can easily understand the interface and its functionality. Most prototyping tools produce the final output in an HTML format so they can be easily shared even if a client is not in the same office where requirements are being developed.
When looking for a prototyping tool, make sure to select a tool which is easy enough to use that you can easily prototype screens while your customer is in the room. This will allow you to brainstorm and make changes to the screens without delays. A prototyping tool should already have common controls already defined to maintain design standards and improve the appearance of your screens. Being able to enter sample data in each screen can allow the customer to pinpoint areas that may be incorrect.