现实世界 软件世界
事物 对象（实体）
职责 职责
行为 函数
关系 关系
It is no exaggeration to say that our software system is a true simulation of the real world. Things in the real world can be simulated as an object in the software world: what responsibilities the thing is assigned in the real world, what responsibilities are assigned in the software world; what characteristics it has in the real world, in the software world What kind of attributes are possessed; what kind of behaviors are possessed in the real world, what functions are possessed in the software world; what kind of relationship exists with which things in the real world, and how they should be related to them in the software world. This is the core idea of object-oriented programming and the core idea of finding domain entities in DDD.