MVC Desgin Pattern

http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller
http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjCTutorial/02Essence/02Essence.html

Model-View-Controller (MVC) is a design pattern that was derived from Smalltalk-80. It proposes three types of objects in an application, separated by abstract boundaries and communicating with each other across those boundaries, as illustrated in Figure 1-2. This is the design pattern behind many designs for object-oriented programs. This design pattern aids in the development of maintainable, extensible, and understandable systems.