File Definition Language (FDL) files define the attributes of
    RMS files. You can use FDL to specify RMS options and parameters
    that can be used when creating a file. If you use the callable
    FDL routines in a program, you can specify most RMS run-time
    options used when opening (or creating) a file and connecting a
    record stream.

    Although you can use FDL with sequential and relative RMS files,
    it is especially useful for defining RMS indexed files. Key
    definitions, area definitions, placement options, and bucket-size
    settings are typical of the information used to define indexed files
    that have optimal run-time performance.

    The following DCL commands invoke utilities that use FDL files:

       ANALYZE/RMS_FILE, CONVERT, CONVERT/RECLAIM, CREATE/FDL, EDIT/FDL

    Refer to the Guide to OpenVMS File Applications and the OpenVMS
    Record Management Utilities Reference Manual for information
    on FDL and the utilities that use FDL. See the OpenVMS Utility
    Routines Manual for information on the routines that use FDL
    files.