> Let's say that "xyz" was derived from "abc",
> let's say that someone updated teh firld
> before you did, and it is now "pqr", and
> this causes teh tableupdate to fail, so you
> therefore Rollback. You now need to recalculate
> in order to get a new value based off "pqr"
> rather than off "abc", otherwise you end up
> with some invalid data. And so we're now back
> where we started: We seem to need a mechanism
> to redo those calculations you did in order
> to modify the field and update with valid data.
Yep, in this case you will need a mechanism like that. And, going back to one of your questions in the previous message, this mechanism will probably need to be written on a case by case basis.