重写：数据库设计主要是对在系统中要求持久性的对象作出说明同时还需要给出ER图。如果一个系统包含了更多的实体或者实体的属性也可以采用分层绘制的方式上层图形描述了各实体之间的相互关系而底层图形描述了各实体之间的具体关系

Database design primarily involves providing descriptions for objects that require persistence within a system, accompanied by an ER diagram. If a system contains a greater number of entities (or entity attributes), a layered approach may be taken, with upper-level graphics depicting the interrelationships between entities, while lower-level graphics describe the specific relationships between entities.