雳求管理的重要性 真的很重要吗? 35: 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 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) 上海交通大学计算机系 16 ∠
上海交通大学计算机系 16 需求管理的重要性 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)
需求分析的重要性 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 350 companies 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 were completed. Moreover, in large companies, only g% of the projects were delivered on time and cost what they were budgeted, and 16% met those criteria in small companies(Standish 1994) 上海交通大学计算机系 17 ∠
上海交通大学计算机系 17 需求分析的重要性 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 350 companies 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 were completed. Moreover, in large companies, only 9% of the projects were delivered on time and cost what they were budgeted, and 16% met those criteria in small companies (Standish 1994)
雳求管理的重要性 To understand why, standish(1995) asked the survey respondents to explain the causes of the failed projects The top factors were reported to be I incomplete requirements (13.1% 2. lack of user involvement(12. 4%) 3. lack of resources(10.6%) 4. unrealistic expectations(9.9%o) 5. lack of executive support (9.3%) 6. changing requirements and specifications(8.7%) 7. lack of planning(8.1%) 8. system no longer needed (7.5%) 上海交通大学计算机系 18 ∠
上海交通大学计算机系 18 需求管理的重要性 To understand why, Standish (1995) asked the survey respondents to explain the causes of the failed projects. The top factors were reported to be 1.incomplete requirements (13.1%) 2.lack of user involvement (12.4%) 3.lack of resources (10.6%) 4.unrealistic expectations (9.9%) 5.lack of executive support (9.3%) 6. changing requirements and specifications (8.7%) 7.lack of planning (8.1%) 8.system no longer needed (7.5%)
需求分析的重要性 ◆5点事实 软件生命周期中,一个错误发现得越晚,修复错误的 费用越高 表5-1生命周期中修复软件的相对费用 阶段 相对修复费用 需求阶段 0,Y~Q.2 设计阶段 5 编码阶段 单元测试阶段 验收测试阶段 维护阶段 20 上海交通大学计算机系 19 ∠
上海交通大学计算机系 19 需求分析的重要性 5点事实 ◼ 软件生命周期中，一个错误发现得越晚，修复错误的 费用越高
雳求管理的重要性 许多错误是潜伏的,并且在错误产生后很长一段时间才被检查出 来 在需求过程中会产生很多错误 o DeMarco在一份研究报告中指出,被检查出来的错误的56%产生的 根源可以追溯到需求阶段。 0 AIRMICS所进行的一项调查发现,在一份美国军方大型管理信息系 统的需求现格说明书(SRS中存在着50多个错误,当然这仅仅是 个软件项目中的一次调查。 在需求阶段,代表性的错误为疏忽、不一致和二义性 o美国海军研究实验室从20世纪70年代起就对软件开发技术不断地进 行研究。得出的研究数据表明:A_T项目中77%的需求错误特点 是不明确:疏忽、不一致和二义性。按错误类型对这些错误分布进 行分析的结果是:49%不正确的事实,31%疏忽,13‰不一致,5 二义性 上海交通大学计算机系 0
上海交通大学计算机系 20 需求管理的重要性 ◼ 许多错误是潜伏的，并且在错误产生后很长一段时间才被检查出 来 ◼ 在需求过程中会产生很多错误 o DeMarco在一份研究报告中指出，被检查出来的错误的56％产生的 根源可以追溯到需求阶段。 o AIRMICS所进行的一项调查发现，在一份美国军方大型管理信息系 统的需求现格说明书(SRS)中存在着500多个错误，当然这仅仅是一 个软件项目中的一次调查。 ◼ 在需求阶段，代表性的错误为疏忽、不一致和二义性 o 美国海军研究实验室从20世纪70年代起就对软件开发技术不断地进 行研究。得出的研究数据表明：A—7E项目中77％的需求错误特点 是不明确：疏忽、不一致和二义性。按错误类型对这些错误分布进 行分析的结果是：49％不正确的事实，31％疏忽，l 3％不一致，5 ％二义性