The RDB$STORAGE_MAPS system table contains information about
    each storage map. The following table provides information on the
    columns of the RDB$STORAGE_MAPS system table.

                                Data
    Column Name                 Type      Summary Description

    RDB$MAP_NAME                char(31)  The name of the storage
                                          map.
    RDB$RELATION_NAME           char(31)  The name of the table
                                          to which the storage map
                                          refers.
    RDB$INDEX_NAME              char(31)  The name of the index
                                          specified in the SQL
                                          clause, PLACEMENT VIA
                                          INDEX, of the storage map.
    RDB$FLAGS                   integer   Flags.
    RDB$MAP_SOURCE              list      The user's source text for
                                of byte   the storage map definition.
                                varying
    RDB$DESCRIPTION             list      A user-supplied description
                                of byte   of the storage map.
                                varying
    RDB$EXTENSION_PARAMETERS    list      Lists the column names
                                of byte   for vertical record
                                varying   partitioning.
    RDB$VERTICAL_PARTITION_     integer   A counter that indicates
    INDEX                                 the number of vertical
                                          record partitions.

                                          If vertical record
                                          partitioning is used, there
                                          is one RDB$STORAGE_MAPS for
                                          each vertical partition.
    RDB$VERTICAL_PARTITION_     char(31)  Name of the vertical record
    NAME                                  partition.
    RDB$SECURITY_CLASS          char(20)  Reserved for future use.