The action of the CHANGE RELATION statement with the CHANGE
    option depends on the change-clause as follows:

    o  CHANGE field-name BASED ON global-field-name-gives the
       specified field the attributes of another field

    o  CHANGE field-name dtr-clause-changes DATATRIEVE support
       characteristics

    o  DELETE CONSTRAINT constraint-name-deletes a relation-specific
       constraint from the relation definition

    You can specify local DATATRIEVE support clauses on any of these
    fields. For more information on the DATATRIEVE clauses, ask for
    HELP on Field_attr.