class PivotI extends AbstractPivotI {
    // no attributes on this class
    // methods
}
class abstract AbstractPivotI {
    Integer id;
}
class BoI extends AbstractBoI {
    // no attributes too
    // some methods
}
class abstract AbstractBoI {
    @JMap(attributes={"id"}
          classes   ={PivotI.class })
    Integer boIfield;
}
class Magic {
    public void whereTheMagicHappens() {
        //some magic code 
        PivotI source = new PivotI(1);
        RelationalJMapper<BoI> mapper = new RelationalJMapper<BoI>(BoI.class);
        BoI destination = mapper.manyToOne(source);
        //more magic code
    }
}