Task 8

SCHEMA people;
    ENTITY person;
        first_name: STRING;
        last_name: STRING;
    END_ENTITY;
END_SCHEMA;
SCHEMA library;
    REFERENCE FROM person;
    ENTITY book;
        number: INTEGER;
        author: person;
        name: STRING;
        UNIQUE
            id: number
        WHERE
            n: number > 0
    END_ENTITY;
END_SCHEMA.