You may use the two-phase commit protocol in RDML to distribute
    transactions. To use the two-phase commit protocol with RDML,
    you must either recompile any existing application programs that
    were compiled with Oracle Rdb V3.1 or earlier, or you must write new
    application programs. With RDML, the two-phase commit protocol is
    not the default.

    RDML provides the following ways for application programs to use
    the two-phase commit protocol:

    o  By implicitly calling DECdtm system services calls in either
       of two ways:

       -  Using the /DISTRIBUTED_TRANSACTION qualifier in the
          precompiler command line

       -  Using the DISTRIBUTED_TRANSACTION keyword in the
          START_TRANSACTION statement

    o  By explicitly calling the DECdtm system service calls
       and using variables to pass the value of the distributed
       transaction identifier (TID)

       If your application starts a distributed transaction that
       includes other read/write database management products that
       support the two-phase commit protocol, your application
       must explicitly invoke the DECdtm system service calls. For
       example, if your application starts a distributed transaction
       using Oracle Rdb and Oracle CODASYL DBMS, your application must
       explicitly call SYS$START_TRANS and SYS$END_TRANS.

       In addition, you must use the full DISTRIBUTED_TRANSACTION
       clause in the START_TRANSACTION statement.

    The implementation of RDML with distributed transactions is
    very similar to using RDBPRE with distributed transactions. See
    the "Oracle Rdb Guide to Distributed Transactions" for a complete
    description of using RDBPRE with distributed transactions and the
    "RDML Reference Manual" and the "Guide to Using RDO, RDBPRE, and
     RDML" for more information.