Transactions ISOLATIONS level

Hi all,
I'm studying transactions isolation levels. I have some questions, hope somebody will help me:

1. How can I change the transaction isolation level via SQL - PL/SQL ? ( I mean without administrator's tools)
2. When I issue a SELECT FOR UPDATE the transaction level switches automatically to TRANSACTIONS_SERIALIZABLE ?
3. I understand row locking and table locking but what does it mean "page" locking ??

Thanks a lot in advance
Francesco Received on Wed Jun 27 2001 - 09:13:35 CDT