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Making Software by Greg Wilson, Andy Oram

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Does the Cost of Fixing Software Increase over the Project Life Cycle?

The significance of the first question has been expressed well by Agile methods pioneer Kent Beck in his book Extreme Programming Explained [Beck 1999]:

Figure 10-1 is “the technical premise for XP” (eXtreme Programming). If the cost of making a software change “rose slowly over time...you would make decisions as late in the process as possible...and...only implement what you need to.”

However, “if a flattened cost curve makes XP possible, a steep change cost curve makes XP impossible.”

The cost of change may not rise dramatically over time

Figure 10-1. The cost of change may not rise dramatically over time

We can therefore ask whether XP or other Agile methods can ensure a flattened cost-of-change curve. We can also ask what other strategies can flatten the curve—so that late fixes do not threaten a project’s costs and delivery dates—as well as how to reduce fixes for projects that have a steep cost-to-fix curve. This chapter will provide some answers to these questions.

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