Layering
分层，抽象。它是一个很重要的概念，在计算机科学的其他领域（通信等）都有应用。
Layering has Hierachy.
Abstract:
为什么叫抽象？将什么东西抽象了？
Example: 去订票网站查询机票价格，the platform provides a service layer on top of each airline, abstracting away the details of each airline’s details for you.
The separation allows each layer in the hierachy to focus on doing its job well, and provide a well-defined service to the layer above.
Service: up and down, with a well-defined interface between layers.
provides clear separation of concerns. 比如说，这一整条链路中，我们可以使用其他的编译器，比如pycharm到spyder。
其中，#6 is a specific advantange in computer networks.
Reference:
- Course
- Self-contained: 自包含特性指的不需要其它基本数据单元的协助，就能够成功地完成解码。编译等工作