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Bays, Michael, Software Release Methodology, Englewood Cliffs, N.J.: Prentice Hall, 1999. This book discusses software configuration management with an emphasis on releasing software into production. Bersoff, Edward H., and Alan M. Davis. Impacts of Life Cycle Models on Software Configuration Management. Communications of the ACM 34, no. 8 (August 1991): 104 118. This article describes how SCM is affected by newer approaches to software development, especially prototyping approaches. The article is especially applicable in environments that are using agile development practices.

Managing a software project is one of the formidable challenges of the twentyfirst century, and estimating the size of a project and the effort required to complete it is one of the most challenging aspects of software-project management. The average large software project is one year late and 100 percent over budget (Standish Group 1994, Jones 1997, Johnson 1999). This has as much to do with poor size and effort estimates as with poor development efforts. This section outlines the issues involved in estimating software projects and indicates where to look for more information.

further reading on scheduleestimation techniques, see 8 of Rapid Development (McConnell 1996) and Software Cost Estimation with Cocomo II (Boehm et al 2000).

You can estimate the size of a project and the effort required to complete it in any of several ways: Use scheduling software. Use an algorithmic approach, such as Cocomo II, Barry Boehm s estimation model (Boehm et al 2000). Have outside estimation experts estimate the project. Have a walkthrough meeting for estimates. Estimate pieces of the project, and then add the pieces together. Have people estimate their own pieces, and then add the pieces together. Estimate the time needed for the whole project, and then divide up the time among the pieces. Refer to experience on previous projects. Keep previous estimates and see how accurate they were. Use them to adjust new estimates.

Pointers to more information on these approaches are given in the Additional Resources subsection at the end of this section. Here s a good approach to estimating a project:

Software Engineering Economics (Boehm 1981).

Establish objectives What are you estimating Why do you need an estimate How accurate does the estimate need to be to meet your objectives What degree of certainty needs to be associated with the estimate Would an optimistic or a pessimistic estimate produce substantially different results Allow time for the estimate, and plan it Rushed estimates are inaccurate estimates. If you re estimating a large project, treat estimation as a miniproject and take the time to miniplan the estimate so that you can do it well. Spell out software requirements Just as an architect can t estimate how much a pretty big house will cost, you can t reliably estimate a pretty big software project. It s unreasonable for anyone to expect you to be able to estimate the amount of work required to build something when something has not yet been defined. Define requirements or plan a preliminary exploration phase before making an estimate. Estimate at a low level of detail Depending on the objectives you identified, base the estimate on a detailed examination of project activities. In general, the more detailed your examination is, the more accurate your estimate will be. The Law of Large Numbers says that the error of sums is greater than the sum of errors. In other words, a 10 percent error on one big piece is 10 percent high or 10 percent low. On 50 small pieces, 10 percent errors are both high and low and tend to cancel each other out.

It s hard to find an area of software development in which iteration is not a valuable technique. This is one case in which iteration is useful. For a summary of iterative techniques, see Section 34.8, Iterate, Repeatedly, Again and Again.

Use several different estimation techniques, and compare the results The list of estimation approaches at the beginning of the section identified several techniques. They won t all produce the same results, so try several of them. Study the different results from the different approaches.

Children learn early that if they ask each parent individually for a third bowl of ice cream, they have a better chance of getting at least one yes than if they ask only one parent. Sometimes the parents wise up and give the same answer; sometimes they don t. See what different answers you can get from different estimation techniques. No approach is best in all circumstances, and the differences among them can be illuminating. For example, on the first edition of this book, my original eyeball estimate for the length of the book was 250-300 pages. When I finally did an indepth estimate, the estimate came out to 873 pages. That can t be right, I