Software Modeling learning experience

User definitions in the system are not specific to people,
It is used for anything in the operating system.
The role concept must come from the human concept, but it does not mean that it must be assumed by a person!
For example:
The role of the reviewer in the library management system,
The examiner is responsible for checking the validity of all library books,
However, people do not assume this role, because too many books need to be verified, so the system itself assumes this role.

This is a user in UML.
It is not a user, but whether it can benefit or contribute to the system.

Software Modeling Step 1:
Describe the system based on the customer's needs, extract the terms of the description text, and determine the classes that may be used.
Define User Roles Based on beneficiaries and contributors.
Establish associations between classes based on actions of beneficiaries and contributors.
Determine the message transmission between classes.

Step 2 of Software Modeling:
Abstract class to improve the abstract relationship between classes and establish a more rational relationship between classes
What is a class and what class is used for a class?
Is
Use
Relationship
Inheritance and combination .....
It is recommended that you do not use the inheritance mode. Even if the inheritance mode is used, you do not need to inherit classes but interfaces.