分层架构思想

• When thinking of a system in terms of layers, you imagine the principal subsystem in the software arranged in some form of layer cake,where each layer rests on lower layer. In this scheme the higher layer uses various services defined by lower layer,but lower layer is unaware of the higher layer. Furthemore, each layer usally hides its lower layers from the layers above.

• 当我们说一个系统是分层架构的时候，你可以把这个软件想象成一个有很多层的蛋糕的样子，其中每一层放在它的下一层上。较高层使用诸多较低层定义和提供的服务，但较低层并没有察觉较高层的存在。另外，每一层都会对其上层隐藏更低的层。