update field table.....

Hi all,
i'm student from Indonesian.... :)
nice to meet the group....this is my first email in this forum....and i've a
lot of questions about Postgres....
well, one of my problem now is:
i want to update some of my field on table...
--------------------
sem           period
--------------------
 3          2000/2001
 and i want it will be updated automatically to be.....
--------------------
sem           period
--------------------
 4          2001/2002
if date on the system or server (Postgres) changed on if the month changed
from February to March....and it'll also be update...
--------------------
sem           period
--------------------
 5          2002/2003
if the month change from Agustus to September....
is it possible to do this with Postgres? If there's someone ever had
experienced like this, i will be grateful for your help.
thank's for the help...sorry...my english bad and i hope it'll
understandable.... :)
piece...
Rusydi