Oracle 18c

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CREATE TYPE T_Personne;
CREATE TYPE T_SET_Tag AS TABLE OF Varchar2(30);
CREATE TYPE T_Message AS OBJECT (
    Texte Varchar2(500),
    DateEcrit Date,
    Tags T_SET_Tag
);
CREATE TYPE T_SET_Message AS TABLE OF T_Message;
CREATE TYPE T_Contact AS OBJECT(
    Per REF T_Personne,
    Depuis Date
);
CREATE TYPE T_SET_Contact AS TABLE OF T_Contact;
CREATE OR REPLACE TYPE T_Personne AS OBJECT (
    Prenom Varchar2(30),
    Suit T_SET_Contact,
    Ecrit T_SET_Message
);
CREATE TABLE TAB_Personne OF T_Personne
    NESTED TABLE Suit STORE AS TAB_suit,
    NESTED TABLE Ecrit STORE AS TAB_ecrit(
        NESTED TABLE Tags STORE AS TAB_Tags
    );
INSERT INTO TAB_Personne VALUES( 
    'Baam',
    T_SET_Contact(),
    T_SET_Message()
);
1 rows affected

INSERT INTO TAB_Personne VALUES( 
    'Rachel',
    T_SET_Contact(
        T_Contact(
            (SELECT REF(P)
            FROM TAB_Personne P
            WHERE P.Prenom='Baam'), 
            to_date('01/01/2018', 'dd/mm/yyyy')
        )
    ),
    T_SET_Message(
        T_Message(
            'Paris candidat aux jeux Olympiques 2022',
            to_date('01/06/2019', 'dd/mm/yyyy'),
            T_SET_Tag('JM2022')
        )
    )
);
1 rows affected