Service Contract ---  Specifies the description of methods 
which our service will provide to consuming application.
For WCF to identify contracts for the service,We need to 
use a interface/class with [ServiceContract] attribute.
In WCF we can do interface/Class level programming. 

Operation Contract --- We need to expose some methods to 
consuming application to use our services.Those methods 
will have [OperationContract] attribute. Making them public 
will not make them accessible from outside.
So OperationContract Specifies the methods can be 
accessible from outside.