The RDB$FIELD_VERSIONS system table is an Oracle Rdb extension.
    This table contains one row for each version of each column
    definition in the database. The following table provides
    information on the columns of the RDB$FIELD_VERSIONS system
    table.

                                Data
    Column Name                 Type      Summary Description

    RDB$RELATION_ID             integer   The identifier for a table
                                          within the database.
    RDB$FIELD_ID                integer   An identifier used
                                          internally to name the
                                          column represented by this
                                          row.
    RDB$FIELD_NAME              char(31)  The name of the column.
    RDB$VERSION                 integer   The version number for the
                                          table definition to which
                                          this column belongs.
    RDB$FIELD_TYPE              integer   The data type of the column
                                          represented by this row.
                                          This data type must be
                                          interpreted according to
                                          the rules for interpreting
                                          the DSC$B_DTYPE field of
                                          class S descriptors (as
                                          defined in the OpenVMS
                                          Calling Standard).

                                          Segmented strings require
                                          a unique field type
                                          identifier. This identifier
                                          is currently 261.
    RDB$FIELD_LENGTH            integer   The length of the column
                                          represented by this
                                          row. This length must be
                                          interpreted according to
                                          the rules for interpreting
                                          the DSC$W_LENGTH field
                                          within class S and SD
                                          descriptors (as defined
                                          in the OpenVMS Calling
                                          Standard).
    RDB$OFFSET                  integer   The byte offset of the
                                          column from the beginning
                                          of the row.
    RDB$FIELD_SCALE             integer   For numeric data types,
                                          the scale factor to be
                                          applied when interpreting
                                          the contents of the column
                                          represented by this row.

                                          This scale factor must be
                                          interpreted according to
                                          the rules for interpreting
                                          the DSC$B_SCALE field of
                                          class SD descriptors (as
                                          defined in the OpenVMS
                                          Calling Standard).

                                          For date-time data
                                          types, RDB$FIELD_SCALE
                                          is fractional seconds
                                          precision. For other non-
                                          numeric data types,
                                          RDB$FIELD_SCALE is 0.
    RDB$FLAGS                   integer   Flags.
    RDB$VALIDATION_BLR          list      The BLR that represents the
                                of byte   SQL check constraint clause
                                varying   defined in this version of
                                          the column.
    RDB$COMPUTED_BLR            list      The BLR that represents the
                                of byte   SQL clause, COMPUTED BY,
                                varying   defined in this version of
                                          the column.
    RDB$MISSING_VALUE           list      The BLR that represents the
                                of byte   SQL clause, MISSING_VALUE,
                                varying   defined in this version of
                                          the column.
    RDB$SEGMENT_LENGTH          integer   The length of a segmented
                                          string segment. For date-
                                          time interval fields, the
                                          interval leading field
                                          precision.
    RDBVMS$COLLATION_NAME       char(31)  The name of the collating
                                          sequence for the column.
    RDB$ACCESS_CONTROL          list      The access control list for
                                of byte   the column.
                                varying
    RDB$DEFAULT_VALUE2          list      The SQL default value.
                                of byte
                                varying
    RDBVMS$SECURITY_AUDIT       integer   A bit mask that indicates
                                          the privileges that will be
                                          audited for the database,
                                          as specified in the RMU Set
                                          Audit command.
    RDBVMS$SECURITY_ALARM       integer   A bit mask that indicates
                                          the privileges that will
                                          produce alarms for the
                                          database, as specified in
                                          the RMU Set Audit command.
    RDB$FIELD_SUB_TYPE          integer   A value that describes the
                                          data subtype of RDB$FIELD_
                                          TYPE as shown in Help topic
                                          RDB$FIELD_SUB_TYPE.
    RDB$SECURITY_CLASS          char(20)  Reserved for future use.