Oracle Rdb defines a special name to refer to the segments of a
    segmented string. This value expression is equivalent to a field
    name; it names the fields or segments of the string. Furthermore,
    because segments can vary in length, Oracle Rdb also defines a name
    for the length of a segment. These names are:

    o  RDB$VALUE

       The value stored in a segment of a segmented string

    o  RDB$LENGTH

       The length in bytes of a segment

    When using the RDML and RDBPRE precompilers, be sure to define
    a sufficiently large value for the RDMS$BIND_SEGMENTED_STRING_
    BUFFER logical name. An adequate buffer size is needed to store
    large segmented strings (using segmented string storage maps)
    in storage areas other than the default RDB$SYSTEM storage area.
    The minimum acceptable value for the RDMS$BIND_SEGMENTED_STRING_
    BUFFER logical name must be equal to the sum of the length of
    the segments of the segmented string. For example, if you know
    that the sum of the length of the segments is one megabyte, then
    1,048,576 bytes is an acceptable value for this logical name.

    You must specify the logical name value because when RDML and
    RDBPRE precompilers store segmented strings, Oracle Rdb does not
    know which table contains the string until after the entire
    string is stored. Oracle Rdb buffers the entire segmented string,
    if possible, and does not store it until the STORE statement
    executes.

    If the segmented string remains buffered, it is stored in the
    appropriate storage area. If the string is not buffered (because
    it is larger than the defined value for the logical name or the
    default value of 10,000 bytes), it is not stored in the default
    storage area and the following exception message is displayed:

    %RDB-F-IMP_EXC, facility-specific limit exceeded
    -RDMS-E-SEGSTR_AREA_INC, segmented string was stored incorrectly

    To avoid this error, set the value of the RDMS$BIND_SEGMENTED_
    STRING_BUFFER logical name to a sufficiently large value. Note
    that a value of up to 500 MB can be specified for this logical
    name.