Description of the illustration ds_recursion.gif
This figure describes recursion patterns. In the top box, two simple data element recursion patterns appear, and both are invalid because a data element cannot resolve to a primitive data type.
In the bottom box, three valid patterns appear. In the first pattern, a structure derives from itself. A structure cannot derive from itself, however, if it has a child structure. In the second pattern, structure B includes child structure C. Child structure C derives from itself and has a child element named D, from which structure B derives. In the third pattern, structure E has a child structure F, which has a child structure G, which has a child structure E, from which the parent structure E derives.