All structural object classes are subclasses, directly or indirectly, of a single abstract object class, which is called top. Every object represented in the directory belongs to top and, as a result, every entry must have an objectClass attribute. When you create a new class, you must specify the superclass. If you are not creating a subclass of an existing class, the new class is a subclass of top. The parent object becomes a superclass of the new object. Superclass is a classSchema object from which one or more other classSchema objects inherit information. The inherited information includes mandatory and optional attributes (systemMust-Contain, mustContain, systemMayContain, and mayContain) and its parent classes in the directory hierarchy (systemPossSuperiors and possSuperiors).