er time
在需求的问题上有这样一些观点：
1、到达需求的完整性会束缚系统设计。
2、需求分析和验证比较困难。
3、改变需求会消耗额外的时间。
Many requirements errors are passed undetected to the later stages of the life cycle and correcting those errors during or after implementation phase is found to be extremely costly.
许多未被发现的需求错误被传递到生命周期的后继阶段，在后继阶段更正这些错误将花费更多。
Problems of RE can be grouped into three categories：。 Problems of scope， in which requirements may address too little or too much information。 Problems of understanding o Users have incomplete understanding of their needs o Analysts have poor knowledge of problem domain o Ease of omitting “obvious” information o Conflicting views of different users o Vague and un-testable requirements e.g. “user friendly” & “robust”
Problems of volatility i.e. changing/evolving nature of requirements
需求捕获的问题可以分为三类：
范围的问题，需求陈述的信息过多或是过少。
理解的问题：用户不完全理解自己的需要需求分析人员对于问题域缺乏足够的知识忽略一些“明显”的信息。
不同用户的看法有冲突语句含糊和无法测试的需求。例如“用户界面友好”或“高性能”
需求不稳定的问题。例如需求本身的改变/拓展。
Elicitation techniques need to be broad enough to establish the boundary conditions for the target system， and yet focus on creation of requirements as opposed to design activities. RE must begin with an organizational and contextual analysis to determine the objectives and boundary of the target system. Avoiding contextual issues may result in incomplete， unusable and un-verifiable requirements.
捕获需求的范围应比较宽广，这样可以为目标系统制定一个适当的边界。捕获需求注重于产生需求而不是设计活动。捕获需求一般从组织结构和上下文范围开始分析，来界定目标系统的边界。要避免上下文范围问题可能导致的不完全，不可用和无法验证的需求。
Elicitation must focus on creation of requirements， not design activities in order to adequately address the users‘ concerns. Focus on broader design activities improperly