Consider the scenario below and write down a hierarchical task analysis for a cell phone interface.

John decides to ring a friend in his electronic phone book

John presses the left arrow key

The phone display says 'phone book'.

He presses 'YES'

The phone display says 'recall'

He presses 'YES'

The phone display says 'pos?' (requesting position in phone book)

John enters the shortcut digit for his friend.

The digit appears on the phone display

John presses 'YES'

The phone display says 'calling'

A few seconds later it says 'connected'

John talks to his friend

When they finish talking John presses 'NO' to finish the call