Dependency Inversion Principle states that we should decouple high level modules from low level modules, introducing an abstraction layer between the high level classes and low level classes.
依赖倒置原则声明了我们应该将高层模块和低层模块解偶，在高层类和低层类之间引入一个抽象层。
I hope this series introducing the essential modules of the Spring framework has been useful to you.
我希望介绍Spring框架核心模块的这一系列对您有所帮助。
There're several parts such as introducing the function analysis of this system, the partition of function modules, the design principles and realization of the database.
接着，本文介绍了该系统的需求分析及数据库的设计，包括系统功能分析，功能模块的划分及数据库设计的原则与具体设计实现；
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