First, the system framework
System architecture: refers to the integration of large structural applications program.
The system structure is often mentioned, there are two: three-tier architecture and MVC. These two structures both different, but related.
But the use of two structures, both in order to reduce the coupling between system modules.
1.1 three-tier architecture
Three-tier architecture means: the view layer View, Service Layer Service, and the persistence layer Dao. They perform different functions, respectively.
View layer: code for receiving a request submitted by a user's written here.
Service layer: The main business logic is done here.
Dao layer: operation of the database code directly written here.
In order to reduce the degree of coupling between the layers in the three-tier programming using abstract-oriented programming. That is, the upper
call to lower, is achieved through the interface. The lower the upper layer of real service provider, it is to achieve the lower class interface.
Service standard (interfaces) are identical, (implementation class) can be replaced by a service provider. This enables decoupling between the layers.