7.9 Revisions

Although the program is officially finished, you are not finished with it. After it is in use for a few months, someone will come to you and ask, "Can you add a modulus operator?" So you revise the specifications, add the change to the program, update the test plan, test the program, and release it again.

As time passes, more people will come to you with additional requests for changes. Soon the program has trig functions, linear regressions, statistics, binary arithmetic, and financial calculations. The design is based on the idea of one-character operators. Soon you find yourself running out of characters to use. At this point the program is doing work far beyond what it was initially designed to do. Sooner or later you reach the point where the program needs to be scrapped and a new one written from scratch. At this point you write a new Preliminary Specification and start the process over again.