Figure 1.6, “ Inventor Class Tree Summary (Part 1 of 3) ” summarizes the Inventor class tree. Base classes are at the left, and derived classes are at the right. SoBase SoBase SoBase is the base class for SoFieldContainer SoFieldContainer SoFieldContainer , from which both nodes and engines are derived. Action classes are derived from SoAction SoAction SoAction . SoXtComponent is another base class. The Xt render area, as well as the viewers and editors, are all derived from SoXtComponent . Classes to the right in the tree inherit the fields and methods of the classes they are derived from.