Web Dynpro is based on MVC (Model-View-Controller) architecture.
|Model||Objects which can communicate with database.|
|Controller||Controller is an interface between View and Model.|
Models are objects which contains business logic statements to read or write data into database.The models can be developed in the form of Function Modules, BAPI`s, Classes etc.
View is a screen displayed in browser.
Controller is an interface between model and the view, it is responsible for taking the input from screen and it submits to the model, the model will communicate with the database and gives back the result to controller, which intern submits the result to the screen.