db-field               A database field value expression. A
                           database field value expression is a field
                           name qualified with a context variable.
                           The database field must be defined in
                           the current context of the statement.
                           For example, the database field must be
                           defined in the context of the START_STREAM
                           or DECLARE_STREAM statements or the FOR
                           loop. See the DB_Field help entry for more
                           information.