The optional parameters of the external routine. For each
    parameter you can specify a parameter access mode (IN, OUT, and
    INOUT), a parameter name, a data type, and a passing mechanism
    (by DESCRIPTOR, LENGTH, REFERENCE, or VALUE).

    The parameter access mode (IN, OUT, and INOUT) is optional and
    specifies how the parameter is accessed (whether it is read,
    written, or both). IN signifies read only, OUT signifies write
    only, and INOUT signifies read and write. The parameter access
    mode defaults to IN.

    Only the IN parameter access mode may be specified with
    parameters to an external function. Any of the parameter access
    modes (IN, OUT, and INOUT) may be specified with parameters to an
    external procedure.

    The optional parameter name is prefixed with a colon (:).
    The parameter name must be unique within the external routine
    parameters.

    The data type is required and describes the type of parameter
    using either an SQL data type or a domain name.

    You cannot declare a parameter as the LIST OF BYTE VARYING data
    type.