It is true that many experts and scholars in this fields have been addressing this issue, but each supports his own pet theory with its own strengths and weaknesses, and there is no officially sanctioned or generally acknowledged standard.
固然有不少這方面的專家學者致力於此，但仍然群雄割據，各有利弊，並且沒有一套是被公定或公認肯定的。