The name of the storage area that will hold all segmented
    strings. For a single file database or multifile database, if you
    do not explicitly define a storage area for segmented strings,
    segmented strings will be stored in the default storage area,
    RDB$SYSTEM. If your database is a single-file database and you
    specify a storage area other than RDB$SYSTEM, you receive an
    error message because RDB$SYSTEM is the only storage area in a
    single-file database.

    The page format for the segmented string storage area can
    be UNIFORM or MIXED. However, Rdb recommends that if you
    store segmented strings in a MIXED storage area, that area
    contain only segmented strings.