High Quality Content by WIKIPEDIA articles! The Composite UI Application Block (or CAB) is an addition to Microsoft`s .NET Framework for creating complex user interfaces made of loosely coupled components. Developed by Microsoft`s patterns practices team, CAB is used exclusively for developing Windows Forms. A derivative version of CAB exists in both the Web Client and Mobile Client Software Factories as well. It encourages the developer to use either the Model-View-Controller or Model-View-Presenter architectural pattern, to encourage reuse of the individual User Controls (referred to in CAB as "SmartParts") by not coupling them with their underlying data elements or presentation code.