A concept that represents a set of ideas, abstractions, or things in the real world that can be identified with explicit boundaries and meaning and whose properties and behavior follow the same rules. It may be either a single or a group of associated concepts, abstractions, or things.

A quality common to all members of an object class. A property may be any feature that humans naturally use to distinguish one individual object from another. It is the human perception of a single quality of an object class in the real world. It is conceptual and thus has no particular associated means of representation by which the property can be communicated.

Allows expressing the value set that must be stored internally by the system (as distinct from the base value set which defines values for exchange).

Expresses the linkage between the internal codes used for storage and the codes used for exchange.