不锈钢护栏施工方案.doc

软件需求分析的重要性
软件需求分析的困难性
软件需求分析的任务
软件需求分析的过程
软件需求分析的原则
结构化分析方法
原型化方法
补充:有关数据库的基本概念
第三章软件需求分析
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需求分析
需求分析是软件定义时期的最后一个阶段
回答“系统必须做什么?”的问题
系统分析员的主要焦点是“做什么(what)”,不是“怎样做(how)”
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需求分析的重要性
真的很重要吗?
例:Our real-time example is based on the embedded software in the Ariane-5, a space rocket belonging to the European Space Agency (ESA). On June 4, 1996, on its maiden flight, the Ariane-5 was launched and performed perfectly for approximately 40 seconds. Then, it began to veer off course. At the direction of an Ariane ground controller, the rocket was destroyed by remote control. The destruction of the uninsured rocket was a loss not only of the rocket itself, but also of the four satellites it contained; the total cost of the disaster was $500 million (Newsbytes home page 1996; Lions et al. 1996).
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The reason: there was no discussion in the requirements documents of the ways in which the Ariane-5 trajectory would be different from Ariane-4.
统计资料:
In 1994, the Standish Group surveyed over panies about their over 8000 software projects to find out how well they were faring. The results are sobering. Thirty-one percent of the software projects were canceled before they pleted. Moreover, in panies, only 9% of the projects were delivered on time and cost what they were budgeted, and 16% met those criteria