can be shown. Projects with an ROI of over 3 years require some other justification. For example, if a company will go out of business if the project is not done, then the investment in the project may be essential, even if the rate of re- turn is low. For example, the cost of a North American time division multiple access (TDMA) cellular provider switching to third-generation (3G) CDMA may be very high, but it may be essential in order to compete and to stay in business. For any new system design, as well as for redesign, repair, or upgrade, we may be asked to prepare a business case justifying our engineering choices by showing busi- ness benefits. There is a significant difference between a business case for initial de- sign and a business case for redesign, repair, or upgrade. If a decision is made during design, it is a choice among options: Which way will we do this? As a result, the com- parison may be among different outcomes for more than one equal-cost alternative or may be among alternatives with different costs. Any of these options can be compared with the option of doing nothing and not creating the new system at all. However, if a choice is being made regarding changes to an existing system, then options must still be compared with the option of doing nothing, but this option itself has a set of costs associated with it. For example, if the current system has an inter- mittent failure, then the costs of fixing the failure each time it occurs and of losing busi- ness during times of failure need to be factored into our thinking. If a permanent re- pair or upgrade will cost less than repeated failures, then it might be worth doing. Otherwise, it may be less expensive to live with the intermittent failure. One of the most useful engineering tools for project planning and system modeling is the IEEE standard for a software quality metrics methodology (IEEE-1992). Although Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Compa