>I can easily see the need to acquire the lock only when
>the user presses "Save".
If you do that then you're again in a situation where you can undo
the changes of other users or need to go through tedious manual
conflict checking and need to provide a usable interface for this
(that keeps on working even when you change your database structure
afterwards etc.)
So you definitely have to acquire the lock when you press [edit] or,
instead of locking, track edited rows by adding them into your
special table at that moment.
Marc