The Model-View-Controller pattern

Wt implements the MVC design pattern in its user interface. With this pattern, user interface is separated from business logic and storage of the data itself (be it in memory, in a database, in files, ...).

The MVC views (such as WTreeView, but also WComboBox and charts) are classes to display the data. The models (inherited from WAbstractItemModel) represent the data itself. The control is everything that you write around the model and the view, to let the data change in response to user actions; the 'business logic'.