"g. calculating if today is the user's birthday or the totals, taxes and shipping charges for shopping cart items . View: This renders the model into a form suitable for interaction, typically a user interface element. MVC is often seen in web apps: the view is the html page and the code which gathers dynamic data for the page. Controller: This responds to events, typically user actions, and invokes changes on the model (but *not* the view). Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention this data access layer. Model Plane Rack It's common to think of an application as having three main layers: presentation (UI), domain,and data access. In MVC, the presentation layer is split into controller and view. "

", view produces a screen listing the shopping cart contents). The view gets its own data from the model (or direct from the data access layer - sometimes there is no domain logic to do). The model should have no direct knowledge of the view. However, the observer pattern can be used to provide some indirection between model and view, allowing the model to notify interested parties of a change. A view object can register itself with the model and listen for changes but the model itself remains view-agnostic. The controller does not pass domain objects (the model) to the view although it might issue a command telling the view to update itself. The user interface waits for further user interactions, which begins the cycle anew. Spitfire Model Are Plane Benefits and liabilities Although widely used, MVC has both advantages and disadvantages compared to other design options, and individual circumstances should be used to choose the most appropriate design. We discuss some of those here. "