UML类图关系（泛化 、继承、实现、依赖、关联、聚合、组合）
http://www.ibm.com/developerworks/cn/rational/rationaledge/content/feb05/bell/
http://wenku.baidu.com/link?url=5GyOTRXvWqDn2ZIFw1hlY1ujHf_5kkxik-Z40WrvLj9bZAVr0PNrdYzmASiemmHQd-Zd7iuUKiX8aKNKoF3VQEhtpBjSa-SAyjUgWIEUOG_