public class A{
    private attrA_1;
    private attrA_2;
    private attrA_3;

    @OneToOne
    private B b;

    @OneToMany
    private Set<C> c;

    //getter e setter
}

public class B{
    private attrB_1;
    private attrB_2;
    private attrB_3;

    //getter e setter
}

public class C{
    private attrC_1;
    private attrC_2;

    //getter e setter
}