ch02 - Chapter 2 WHY THE WATERFALL MODEL DOESNT WORK M...

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17 Chapter 2 W HY THE W ATERFALL M ODEL D OESN T W ORK oving an enterprise to agile methods is a serious undertaking because most assumptions about method, organization, best practices, and even company culture must substantially evolve. While we have noted the benefits that agile software methods provide, we have yet to describe how it is that ag- ile can so dramatically produce these results. For perspective, we first look at the traditional software model, the waterfall model of development, and see why this apparently practical and logical approach to software development fails us in so many circumstances. Figure 2–1 illustrates the traditional model of software development and its basic phases of requirements, design, coding and test, system integration, and operations and maintenance. This model of development has been with the industry for over 30 years. Many believe that the original source of this model can be found in the paper Managing the Development of Large Software Systems by Winston Royce [1970]. However, we also note that Royce’s view of this model has been widely misinterpreted: he recommended that the model be applied after a significant prototyping phase that was used to first better understand the core technologies to be applied as well as the actual requirements that cus- tomers needed! As Winston’s son, Walker Royce, now with IBM Rational, points out [Larman and Basili 2003], He was always a proponent of iterative and incremental development. His paper described the waterfall as the simplest description . . . the rest of the paper describes [iterative practices]. M
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18 C HAPTER 2 W HY THE W ATERFALL M ODEL D OESN T W ORK Even though misinterpreted, this model of development was a substantial improvement over the former model of “code-and-fix, code-some-more, fix- some-more” practices that were common at the birth of our software indus- try. While it is in vogue today to belittle the waterfall model for its ineffec- tiveness and the rigidity that the model implies, it is also true that tens of thousands of successful applications were built using this basic model: first, understand the requirements; second, design a system that can address those requirements; and third, integrate, test, and deliver the system to its users. Although we accomplished great feats, many projects also suffered greatly because our ability to predict when we would deliver quality software be- came suspect at best. Late delivery was common; delivering solutions that both were late and did not fundamentally address the customer’s real needs was also common. Over time, we all came to understand that the “dreaded system integration phase” would not go as well as planned. On the upside, however, the model provided a logical way to approach build- ing complex systems, and it also provided time for the up-front requirements discovery, analysis, and design process that we knew we needed. For these Operation and Maintenance System Integration Coding and Unit Test Design Requirements Time in Months (Example) 0 3 6 9 12 Deadline Figure 2–1 The waterfall model of development
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