What is the best definition of MVC?

The most major mistake I find with peoples understanding of MVC is that they think the pattern encompasses more than it does. More specifically people often think:

• Model = DataBase
• View = HTML
• Controller = Business Logic and everything else.

This is often the way things work in a smaller application but reality MVC is a way to seperate the Business code from the presentation code. The Model does all the real business work. The views provide the look and feel, and the controller maps one to the other.

I trust the MVC definition given here by Martin Fowler. However, you may want to notice the fact that more or less these framework have their own tweak in it. For example a framework like Django is more Model-Template-Controller due to its templating feature.

See Chapter 14 of the book: Patterns of Enterprise Application Architecture, by Martin Fowler.

The section on MVC starts with:

"Model View Controller (MVC) is one of the most quoted (and most misquoted) patterns around. It started as a framework developed by Trygve Reenskaug for the Smalltalk platform in the late 1970s. Since then it has played an influential role in most UI frameworks and in the thinking about UI design."

It also says:

"As I think about MVC I see two principal separations: separating the presentation from the model and separating the controller from the view.

...

Of these the separation of presentation and model is one of the most important design principles in software, and the only time you shouldn't follow it is in very simple systems where the model has no real behavior in it anyway. As soon as you get some nonvisual logic you should apply the separation. Unfortunately, a lot of UI frameworks make it difficult, and those that don't are often taught without a separation.

The separation of view and controller is less important, so I'd only recommend doing it when it is really helpful. For rich-client systems, that ends up being hardly ever, although it's common in Web front ends where the controller is separated out. Most of the patterns on Web design here are based on that principle."

I believe the same thing. As far as I am concerned anything that manages to separate the concerns of the display, the data/business objects and the control of those (initialisation, responding to user input) gets the benefit that MVC seeks to provide.

The aim is to move these items into re-useable components and be able to swap different implementations in and out and also be able to test the individual pieces in isolation. IMO that's what MVC is all about.

This is a pretty good write up of some of the history and popular implementations of the MVC paradigm. We should add the Model - View - ViewModel pattern that is recommended for WPF in there too.