需求分析：研究问题域，产生一个满足用户需求的系统模型，这个系统模型应该能正确的描述问题域和系统责任，并使后续开发阶段的有关人员能根据这个模型继续进行工作-Demand Analysis: To study the problem domain, a user needs to meet the system model, the system model should be able to correct the descr iption of the problem domain and system responsibility, and follow-up stage of development of relevant personnel in accordance with this model to continue its work