#9 Thou shalt plan for change

The best developers and architects plan for change during all phases of the software life cycle. During the course of an average one year development cycle, not only will the design be subject to change, so too will the user requirements, the development tools, the third party software libraries, the DBMS system, the operating system, the hardware, the network, the programmers, and many other aspects of the application that cannot possibly be foreseen or otherwise planned for. Some aspects of change, such as a new release of the operating system, can certainly be planned for by discussing schedules with the vendor and making a decision whether a new release should be installed or not. Sometime during the application's life, however, the underlying operating system will probably have to be upgraded so it's really just a matter of when changes such as these are done. In either case, you still have to plan for the changes.

The longer the expected project lifetime, the more important it is to plan for change. The Cassini mission to Saturn, operated by JPL, was launched in October of 1997. With any luck, the spacecraft will enter orbit around Saturn in 2004. The JPL engineers running the Cassini ground station definitely must plan for changes in hardware and software prior to the spacecraft's encounter with Saturn in 2004. Any company that designs a long lifetime product with an embedded hardware or software component must pay careful attention to planning for change. Back down on earth, for instance, every high-end Xerox printer contains an embedded workstation controller. Typically these workstations are commercial off-the-shelf products with an average lifespan of eighteen months. Xerox high-end printers are designed for five to ten or more years of continuous operation. Xerox must plan for change in the embedded workstation component for each of its printer lines.