DEFAULT TRANSACTION provides a default transaction for the user.
    By default, Oracle Rdb starts a READ WRITE transaction if none is
    explicitly started. Use the DECLARE TRANSACTION or START DEFAULT
    TRANSACTION statement to make use of this definition. You can
    override this clause with a DECLARE or SET TRANSACTION statement.

                                   NOTE

       Oracle Rdb does not permit the RESERVING or EVALUATING
       clauses to appear in the default transaction.