Chapter 7 -- Defining the System Parameters

Chapter 7

"A system is designed to do something, not everything." — Robert Hall, Research Engineer, North American Aviation

The story goes that Bob Hall made this remark to a vice president who was trying to expand the scope of his project for the umpteenth time, and it almost cost Mr. Hall his job. (In system design, as in all else, it pays to know your audience.) Nevertheless, it remains one of the truest remarks I've ever heard about the system design process. If the project is going to be successful, you must be able to describe what you're trying to accomplish and draw reasonable boundaries around the project. If you can't say with reasonable certainty, "We're going to do this; we're not going to do that," I can promise you that what you are going to do is experience big trouble.

There are three steps to this process of definition:

• Determining the goal, not just of the system but of the project as a whole.
• Establishing the system's design criteria, which will be used to judge any trade-offs during design and implementation and also to evaluate the system's success or failure.
• Defining the system scope—what you will and will not attempt to do.