Hi MultiFlyer, thanks for your response.
Yes I am aware about that interline checked baggage rule that was introduced by OW last year. However, Cathay has decided not to follow this rule and it will interline even when pax is booked on separate PNRs as long as the airlines involved are still OW airlines or non-OW airlines that have interline agreement with CX. However, I am doubtful whether AB will do the same or not. I have sent an email to airberlin but it's been a few days and i still haven't received any reply from them.