Although both joe and sarah are registered as users on their local UNIX system, they belong to different departments; joe is a postgrad student in artificial intelligence while sarah is Head of the Math Department. Their respective home directories might be:
/(root)
---------------------
| |
/tmp /usr
|
---------------- ... ----
| | |
/ai /biol /math
| |
------------ -----------------
| |
/joe /staff
------------------
|
/sarah
The full pathname to joe's home directory is /usr/ai/joe; that to sarah's is /usr/math/staff/sarah.