说明：  UAL案例教程，里面汇集了大量的UML例子，学习UML的时候，可以参考这些例子，模仿玩，你的UML也就精通了
(UAL case tutorial, which brings together a large number of examples of UML, UML learning time, you can refer to these examples, imitating play, you also proficient in UML)