The Workplace Shell provides a number of standard object classes such as folders and data files. The user performs his work by interacting with these objects using their context menus or direct manipulation.
In order to extend the range of tasks that a user can perform using the Workplace Shell, it is necessary to add new object classes to his desktop; typically these may be related to specific productivity tools, such as a Spreadsheet object, or to the user's own business, such as Order Form, Parts Catalog, or Customer.
In the ideal, purely object-oriented, user interface, there would no longer be anything that a user would recognize as a program - there would only be objects, all with their own unique behaviors and uses. As long as the user is provided with suitable tools (that is, object classes), he can work out how to accomplish any particular task without having to learn to use an application program specifically designed for that task. What we might loosely call a Workplace Shell application is really no more than a collection of Workplace Shell object classes.
In order for a newly developed object class to be used, it must be registered to the Workplace Shell. The classes are implemented in such a way that each class, or possibly several classes, is contained in a dynamic link library (DLL). Being in a DLL means that an object's methods can be called by Workplace Shell whenever necessary, and also that the code can be shared between multiple instances of the class. Registering a new class informs the Workplace Shell of the existence of the new class, and gives it the name of the DLL containing its methods.
The Workplace Shell itself, and all its classes including any that a user may develop, are written using the System Object Model, a language-independent environment for object-oriented programming. Anyone wishing to develop new Workplace Shell classes must therefore understand SOM, and also be familiar with the existing Workplace Shell classes, from which his new classes must inherit at least some of their behavior.