What is the difference between MVP VS MVVM? Why we are using MVP even though we have three layers: business, data access and presentation? Is there any specific reason to divide the Presentation layer into MVP?
Answer
MVP and MVVM are both derivatives of MVC. MVC is a pattern that separates the user presentation and interaction from the internal representation.
This requires three layers, since tying the user interaction/presentation directly to the internal representation will cause both to bend to conform to each other. In your application, you described these layers as the Presentation, the Business layer, and the Data Access layer. With only those very loose descriptions, you could potentially be describing any of the MVC derivatives, or the original MVC pattern itself.
The key differences between each of the derivatives are the dependencies each layer takes on the other layers, and how tightly they are bound to each other. This article has some details on the differences, though of course it shouldn't be considered authoritative:
http://nirajrules.wordpress.com/2009/07/18/mvc-vs-mvp-vs-mvvm/
"... MVVM is attractive for platforms which support bi-directional binding with less effort. Also a minor tradeoff is ViewModel unlike Presenter can stand on its own (Presenter normally requires a View’s interface)."