<class name="A">
      <id name="id">
         <generator class="sequence">
            <param name="sequence">id_seq</param>
         </generator>
      </id>
        <many-to-one name="backLink"/>
    </class>
    <joined-subclass name="B" extends="A">
        <key column="id"/>
        <set name="as" inverse="true">
            <key column="backLink"/>
            <one-to-many class="A"/>
        </set>
    </joined-subclass>

create table A (id int8 not null, backLink int8, primary key (id))
create table B (id int8 not null, primary key (id))
alter table A add constraint FK41D36BE61D foreign key (backLink) references B
alter table A add constraint FK41D36BE61C foreign key (backLink) references A
alter table B add constraint FK4254F609D6 foreign key (id) references A
create sequence id_seq