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<blockquote><p>MVC consists of three kinds of objects. The Model is the application object, the View is its screen presentation, and the Controller defines the way the user interface reacts to user input. Before MVC, user interface designs tended to lump these objects together. MVC decouples them to increase flexibility and reuse.</p>

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<p>If the view and the controller objects are combined, the result is the model/view architecture. This still separates the way that data is stored from the way that it is presented to the user, but provides a simpler framework based on the same principles. This separation makes it possible to display the same data in several different views, and to implement new types of views, without changing the underlying data structures. To allow flexible handling of user input, we introduce the concept of the <i>delegate</i>. The advantage of having a delegate in this framework is that it allows the way items of data are rendered and edited to be customized.</p>

<tr valign="top" class="odd"><td><img src="images/modelview-overview.png" /></td><td><b>The model/view architecture</b><p>The model communicates with a source of data, providing an <i>interface</i> for the other components in the architecture. The nature of the communication depends on the type of data source, and the way the model is implemented.</p>

<p>The view obtains <i>model indexes</i> from the model; these are references to items of data. By supplying model indexes to the model, the view can retrieve items of data from the data source.</p>

<p>In standard views, a <i>delegate</i> renders the items of data. When an item is edited, the delegate communicates with the model directly using model indexes.</p>

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