7.1.13 subclass: Relative to one or more superclasses ? an object class derived from one or more superclasses. The members of the subclass share all the characteristics of the super classes and additional characteristics possessed by none of the members of those superclasses.
An object class is an identified family of objects, or conceivable objects, which share certain characteristics. Every object belongs to at least one class. An object class may be a subclass of other object classes, in which case the members of the former class, the subclass, are also considered to be members of the latter classes, the superclasses. There may be subclasses of subclasses, etc., to an arbitrary depth.
From 7.3
Each entry contains an indication of the object classes, and their superclasses, to which the entry belongs.
From 8.3
An object class may be derived from two or more direct superclasses (superclasses not part of the same superclass chain). This feature of subclassing is termed multiple inheritance.
12.3 Object class definition
The definition of an object class involves:
a) indicating which classes this object class is to be a subclass of;
b) indicating what kind of object class is being defined;
c) listing the mandatory attribute types that an entry of the object class shall contain in addition to the mandatory attribute types of all its superclasses;
d) listing the optional attribute types that an entry of the object class may contain in addition to the optional attributes of all its superclasses;
e) assigning an object identifier for the object class.