Programming Interfaces 
The user interface controls specified by SAP are sufficient for developing many of the user interfaces for Web applications. They ensure the user sees a standardized screen. However, not all user interfaces are displayed equally in the same format, which means some dynamic programming is required.
A general rule is that classes and interfaces beginning with CL_WD_ or IF_WD_ have been released for application developers.
Classes and interfaces beginning with CL_WDR_ or IF_WDR_ have not been released. These classes are not contained in the package interface and they can change without prior notice. Furthermore, there may be side effects from calling these internal class methods.
Data flow and validation are described in the The Phase Model.
The programming interfaces below support application developers with dynamic programming: