Hi Nikhil,
If your requirement is only for validation, you can think of trying this kind of logic.
In the DO_PREPARE_OUTPUT Method, the flag first_time will be set to true when the view will be loaded for the first time. In that method, you take a snapshot of the Notes Business Object(BO) and extract the data and store it in a static private attribute of the class(an internal table). Later on when the user is done with the changes and presses save then you can again extract the changed values and compare them to figure out the changes.
Well, this is a just another thought while in the mean time I will check the BOL programming methods if there is something with which we can figure out the delta.
Hope this helps.
Thanks,
Samantak.