Kenneth M A.
In a top down approach to system design, the programmer will start by identifying the output that the system will need to produce. There are a number of possible output formats that must be considered, including such items as: printer, screen, plotter, audio, email, links to web pages, automated fax facilities and computer output microfilm. There are many more possible output devices that could be incorporated into any system - it will depend on the technology that is available to the developers.
There are sound reasons for starting the system development with the design of the output. The system will be implemented to help improve efficiencies or to solve a problem. In order to do this, the the first step will be to determine what can be done to help the situation. Once this has been done, a clear picture of what has to be produced can be identified. This will shape the output requirements of the system. While the output may seem to be the last part of the system that should be developed, it should not be. In order to make the system a success it must be able to produce the outcomes that can solve the problem, therefore the output required needs to be identified early in the process.
Once the output has been identified, it will place constraints on the system. These constraints will include requirements of data to be collected to produce the output, and to the limitations imposed by the technologies used to create the output. While it may sound minor, the manner in which output is to be created and/or displayed is actually of great significance to the design of a computer system. This is because it can quickly change the nature of the resources that are required by the system to produce the output. For example, if the system is to collect pictures that are displayed over the web, then the file size will not have to be as large as those that will be printed.
Some of the major constraints on output include:
Printers - the print quality, e.g. Laser/inkjet/colour, and the nature of the information to be produced. For example, if a receipt is to be printed and needs to be made in duplicate, then an impact printer will need to be used or the item printed twice.
Screen - If the output is primarily to be screen based, then the screen will impose a number of limitations on the output. The output will need to be designed to fit into the screen size. If the screen is monochrome, then colour cannot be used, etc.