A simple attribute may have any value from a particular primitive domain. If the value is restricted to two or more primitives, the allowed values are given using this subclass.
Note that this subclass is also used to define restrictions as related to the use of enumerations. The enumerated descriptions are given in a Set construction, with each option in double quotes and spaces between the options.
This subclass may be used by a restricted clause or as the means of expressing class attribute values, as indicated in TupleDefinition.