>>>Ok, that makes sense.
>>>
>>>Under the following scenario:
>>>
>>>User 1 adds 4 detail lines
>>>User 2 adds 3 detail lines
>>>User 2 saves changes.
>>>User 1 attempts to save but is not able to because header record has
>>>been changed by user2 save.
>>>
>>>Since everything for user1 would rollback, they would have to reenter all detail lines
>>>again. Is that correct?
>>>
>>>Thanks again.
>>
>>The detail lines would still be in the cursors/buffers. They could edit things and hit save button again.
>
>Just wonder:-
>
>let say total_qty = 20
>if 10 computer at the same time hit save :
>replace total_qty with total_qty - 1
>
>some fail while some success, will total_qty still have the correct answer ?

What do you think correct answer is? Those that fail will not reduce total qty.

Better approach is to add separate records for each and have backend compute new total.