One of the most powerful features of PowerBuilder is inheritance. It enables you to build windows, user objects, and menus that are derived from existing objects. When you build an object that inherits from another object, you create a hierarchy (or tree structure) of ancestor and descendent objects.
The object at the top of the hierarchy is a base class object, and the other objects are descendants of this object. Each descendant inherits its definition from its ancestor. The base class object typically implements generalized processing, and each descendant modifies the inherited processing as needed.
The PowerBuilder system objects compose such a hierarchy. At the top of the hierarchy is the PowerObject, the base class from which all the objects and controls described in this book descend. The hierarchy also contains other (generic) base class objects that are not typically used in application development but are necessary parts of the logical organization of the hierarchy.
