Introduction to OOP: Chapter 7: Inheritance
Trees versus Forests
There are two common views of class hierarchies:
All classes are part of a single large class hierarchy.
Thus, there is one class that is the original ancestor of all other
Smalltalk, Java and Delphi Pascal do this.
Classes are only placed in hierarchies if they have a relationship -
results in a forest of many small hierarchies, but no single ancestor.
C++, Objective-C, and Apple Object Pascal do this.
Intro OOP, Chapter 7, Slide 16