### Class Hierarchy and Object Structure

Note that class hierarchy is different from object structure. Object structure is the layering of object arrays that was previously described in the DS_C_DS_DN declaration in Building a Name Object. It occurs when one object contains another object as the value of one or more of its attributes.

This is what is meant by recursive objects: one object can point to another object as one of its attribute values. The layering of subobjects below superobjects in this way is described repeatedly in XDS/CDS Object Recipes.

The only practical significance of class hierarchy is in determining all the attributes a certain object class must have. Once you have done this, you may find that a certain attribute requires as its value some other object. The result is a compound object, but this is completely determined by the attributes for the particular class you are looking at.

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