Restricting access to large objects.

I sent with the wrong email first. sorry. 

I can't find any docs / mails on this subject. 
How can I restrict access to large objects. 

1.) Based on users. 
2.) Rules/triggers? 


Thanx. 

Aasmund Midttun Godal 

aasmund@godal.com - http://www.godal.com/ 
+47 40 45 20 46