介绍Uml用例的描述，
UML是数据库设计过程中，在E-R图(实体-联系图)的设计后的进一步建模。要了解一下UML设计中有的图例及基本作用。首先对UML中的各个图的功用做一个简单介绍。(Introduce the descr iption of the Uml use case,
UML is a further modeling of the database design process after the design of the E-R diagram (entity - contact diagram). To understand some illustrations and basic functions in the UML design. First, a brief introduction to the functions of each graph in UML is made.)