how to calculate dates?

hi ,

i will give a short description about my project and what i need from you,In my project the user enters the detail(like expiry date , name, place of issue) of his document which he wants to be notified when the expiry date of the document is with in 30 days.

Example : if his documents expiry date is 12.12.12 the system should sent a notification to him on 12.11.12 that means before 30 days of expiry.

How can i achieve the above scenario?How to trace 30 days and sent notification? As i am a very first beginner of SAP ABAP please explain me in detail.

THANKS IN ADVANCE,

-NAVEEN

Moderator message: very basic, obviously insufficient research -> question status removed

Message was edited by: Thomas Zloch