Controllers  

Controllers are the active parts of a Web Dynpro component. In the design of Web Dynpro controllers, SAP has made a significant modification to the original Model View Controller (MVC) concept of a controller. In broad terms, SAP has defined two categories of Web Dynpro controller:

●      Controllers Having No Visual Interface  

They refer to those parts of the business application that process data (data generators)

●      Controllers Having A Visual Interface  

They refer to those parts of the business application that display data (data consumers)

All controllers lacking a visual interface are primarily responsible for generating data. These data will ultimately be supplied for display to a controller having a visual interface.

More information: Location of Coding