0 used especially in questions when asking about which person owns or is responsible for something:
1 used for adding information about a person or thing just mentioned:
Cohen, whose short film won awards, was chosen to direct the movie .
There was a picture in the paper of a man whose leg had been blown off.
They meet in an old house, whose basement has been converted into a chapel.
Fraud detectives are investigating the company, three of whose senior executives have already been arrested.
2 used to ask which person owns or is responsible for something, or to say who is responsible for something:
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.