logics programing

why interface and abstract =>

• The interface is one that you are used to exposing to the outside, for eg., you are creating a WCF service to connect your consumer, in this case, Interfaces ( function definitions are exposed)
• An abstract is one in which you create an abstraction of your project like top level. For eg., you are creating a logging mechanism abstract layer as public void Log(T request)
• we can override this abstract and make it mold as per our use case.

when we use interface and abstract

• The interface is used in different scenarios like when you are exposed outside when you want to implement the loosely coupled architecture such as using dependency injection. 
• abstract you can use it in making higher level skeleton 

why we need to implement interface 

• typically interface is used to give more flexibility. such as ILog is an interface which may be implemeted in FileLog or may be SqlLog.