Code:
SQL> select objname,
  2     regexp_substr(objname, '[^.]*') owner,
  3     regexp_substr(objname, '[^.]*',1,3) obj_name,
  4     regexp_substr(objname, '[^.]*',1,5) part_name
  5  from obj;

OBJNAME                        OWNER        OBJ_NAME     PART_NAME
------------------------------ ------------ ------------ ------------
busdep                         busdep
busdep.orders                  busdep       orders
busdep.orders.part_1           busdep       orders       part_1