updating database every month

Hi,

I have problem relating to PL/SQL. My problem is i want to update a table in the database on the first day of the every month. Is it possible with Triggers ? if so how? for example iam having a table called CASUAL_LEAVE. I want to update the casual leaves of all the users in the table on every month first.

thanks in advance
regards
phanik.

DBMS_JOB

- Chris