All object classes in a Microsoft® Active Directory® directory service schema are derived from the special class top. With the exception of top, all object classes are subclasses of another object class. For example, contact is a subclass of organizationalPerson; organizationalPerson is a subclass of person; and person is a subclass of top. The subClassOf attribute of a classSchema object is a single-valued property that indicates the immediate superclass of the class.
Some of the attribute values that define a class are inherited from its superclasses. So, the contact class inherits values from its superclasses, which are the organizationalPerson, person, and top classes. A class inherits the following data from its superclasses:
Be aware that object class can also have many auxiliary classes, which are specified in the auxiliaryClass and systemAuxiliaryClass attributes of a classSchema object. An object class inherits mustContain, mayContain, systemMustContain, and systemMayContain values from its auxiliary classes.