How-to extend schema

[Csillag Tamas <cstamas@digitus.itk.ppke.hu>]

Hi,

I want to use ldap as a lookup table for Postfix.
For this purpose, and for internal demands like
  We are a University so I want to define special attribute for account
  lockout, when (s)he applied for submisson to this university, if (s)he
  wants spam filtering etc...

So AFAIK this can be make with extending the schema:
 1. I have to request an OID from IANA
 2. Write the schema myself

This stage I have problems, I do not know how to write the schema
properly. I can copy/ modify already existing files but I want to know
what each line means.
I read: http://www.openldap.org/doc/admin22/schema.html
But it is not enought for me to understand

So if someone can explain me how it works or point me the right Docs i
will be very happy

Thanks in advance.

-- 
cstamas