SQL & PL/SQL

Hi,

I have created a nested table based on the following details:

CREATE TYPE typ_item AS OBJECT --create object
(prodid NUMBER(5),
price NUMBER(7,2) )
/
CREATE TYPE typ_item_nst -- define nested table type
AS TABLE OF typ_item
/
CREATE TABLE pOrder ( -- create database table
ordid NUMBER(5),
supplier NUMBER(5),
requester NUMBER(4),
ordered DATE,
items typ_item_nst)
NESTED TABLE items STORE AS item_stor_tab
/
INSERT INTO pOrder
VALUES (800, 80, 8000, sysdate,
typ_item_nst (typ_item (88, 888)));

Now I would like to create a trigger on table pOrder for after insert or update or delete
and I would like to track the new and old value for the columns inside nested table.
Can anybody direct me how to do it?

I would like to know the sytax for it like:

declare
x number;
begin

x := :new.nestedtablecolumn;--how to get the new and old value from nested table columns
end;

Hope my question is clear.

Thanks,
Lavan