public function set($id_a, $id_b)
 {
     if ($id_a < $id_b) {
         return parent::getId($id_a, $id_b);
     } elseif ($id_a > $id_b) {
         return parent::getId($id_b, $id_a);
     } else {
         return 0;
     }
 }
 protected function getId($idz, $name, $value)
 {
     return parent::getId($idz, $this->a->getId($name, $value));
 }
 public function getId($name, $value)
 {
     return parent::getId($this->an->getId($name), $this->av->getId($value));
 }
 public function getId($pid, $name)
 {
     return parent::getId($pid, $this->zn->getId($name));
 }