Memos, reports, and graphs are examples of kinds of objects that might be grouped together in a folder. Folders differ from other kinds of objects, but all folders share appearance and behavioral characteristics. The folder is a general-purpose container that can hold objects of many different classes. To use a folder, users learn its properties and behaviors. A subclass inherits the properties and behaviors of its parent class.
Developers add new properties and behaviors to subclasses to create desired specializations.
Because the portfolio inherits the folder's properties and behaviors, users can transfer their knowledge of the folder to the portfolio. They need only learn the distinguishing features of the portfolio to take advantage of its benefits. Object classes and subclasses seen by users should be derived directly from analysis of users' tasks and understanding users' goals, motivations, and current techniques. In this way objects presented through the computer interface will be more easily recognized and their rules more readily understood. An object's composition contributes to its class membership and therefore to establishing its properties and behaviors.