让学生掌握用例图的语义、功能，使用事件流描述用例；了解用例和脚本的关系及使用用例图为系统的上下文、系统的需求建模。-Enable students to master the use case diagram semantics, functions, event stream described　understand the relationship between use cases and scr ipts and use cases Pictured system context, the needs of the system modeling.