SQL> select banner from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
PL/SQL Release 12.2.0.1.0 - Production
CORE    12.2.0.1.0      Production
TNS for 64-bit Windows: Version 12.2.0.1.0 - Production
NLSRTL Version 12.2.0.1.0 - Production

SQL> create or replace type t_People as object
  2  (
  3  nPassport number,
  4  sFIO varchar2(50)
  5  ) not final
  6  /

Type created.

SQL> create or replace type t_student under t_People 
  2  (
  3  nStudID number
  4  ) final
  5  /

Type created.

SQL> create table students of t_student 
  2  (constraint pk1 primary key (nStudID)) OBJECT IDENTIFIER IS PRIMARY KEY
  3  /

Table created.

SQL> desc students
 Name                                                                     Null?    Type
 ------------------------------------------------------------------------ -------- -------------------------------------------------
 NPASSPORT                                                                         NUMBER
 SFIO                                                                              VARCHAR2(50)
 NSTUDID                                                                  NOT NULL NUMBER

SQL> alter type t_people drop attribute (sFIO) cascade;

Type altered.

SQL> desc students
 Name                                                                     Null?    Type
 ------------------------------------------------------------------------ -------- -------------------------------------------------
 NPASSPORT                                                                         NUMBER
 NSTUDID                                                                  NOT NULL NUMBER

SQL>