switching locking off?

Hi,

    I am writing a Java program which is supposed to assist in teaching why locking is used in a database system (Oracle). Does any one know if there is any way that I can make Oracle 'switch off' locking, so I can show what problems occur when there is no locks (i.e. lost update problem, inconsistent analyis etc.). I know it is a bit of strange thing to ask a DBMS to do - to actually make its data inconsistent - but is there any way that I can actually do it rather than simulate it?

    Also, is it possible to have a single user have more than more transaction going on at any one time (obviously there has to be 2 transactions for them to interfere with each other), or would it have to be that the user would have to have 2 sessions open at the same time?

    Thanks,

                    Jenny