Initiates a group of statements that Oracle Rdb executes as a unit.
    A transaction ends with a COMMIT or ROLLBACK statement. If you
    end the transaction with the COMMIT statement, all the statements
    within the transaction execute. If you end the transaction with
    ROLLBACK, none of the statements takes effect.

    If an application starts a distributed transaction by explicitly
    calling the DEC/dtm system service SYS$START_TRANS, it must
    complete the transaction by calling the DEC/dtm SYS$END_TRANS
    or SYS$ABORT_TRANS system service.

    Examples:

    Read-only --  START_TRANSACTION READ_ONLY

    Read/write -- START_TRANSACTION READ_WRITE RESERVING -
                     JOB_HISTORY FOR PROTECTED WRITE, -
                     SALARY_HISTORY FOR EXCLUSIVE WRITE -
                   WAIT -
                   EVALUATING JOB_CODE_EXISTS AT VERB_TIME

    Batch-update - START_TRANSACTION BATCH_UPDATE