Class

A <Class> is a <Thing> that is an understanding of the nature of things and that divides things into those which are members of the class and those which are not according to one or more criteria. The identity of a Class is ultimately defined by its members. No two classes have the same membership. However, a distinction must be made between a Class having members, and those members being known, so within an information system the members recorded may change over time, even though the true membership does not change