https://docs.oracle.com/en/database/oracle/oracle-database/26/dbiad/db_cdb.htmlhttps://docs.oracle.com/en/database/oracle/oracle-database/12.2/cncpt/overview-of-the-multitenant-architecture.html#GUID-4311CC75-87D3-4548-A7CE-11FE5141C9E3