update table field value II

Hi,
i'm sorry there's some mistake on my last subject....it's should be...
i want to update some of my field for all records on table...
----------------------------
id         sem           period
----------------------------
A991     3          2000/2001
B992     1          2000/2001

 and i want it will be updated automatically to be.....
----------------------------
 id         sem           period
----------------------------
A991     4          2000/2001
B992     2          2000/2001

if date on the system or server (Postgres) changed from February 2000 to
March 2000....and it'll also be update...
----------------------------
 id         sem           period
----------------------------
A991     5          2001/2002
B992     3          2001/2002

if the month change from September 2000 to February 2001....
is it possible to do this with Postgres?
If there's someone ever had experienced like this, i will be appreciate the
help (Oliver too)
piece...
Rusydi