Relationships among elements at each level are described according to the UML(Unified Modelling Language) specification, the use case textual specification is defined by the extended BNF and its corresponding graphical representations are presented.

• 按照UML规范,定义了各层有关元素间的关系,给出了由扩展巴科斯范式定义的用例描述规范及相应的图形表示。