[tlholaday]

1: Use case. Traditional bookkeeping. Asset account balances start at zero initially, then increase with every debit and decrease with every credit. If someone mis-reads a check and enters a deposit as $200 instead of as $20, we do not change the $200 to $20. Instead, we do one of two things: reverse the difference with a $180 credit, or reverse the deposit with a $200 credit followed by a new $20 debit. Traditional DBs support all three approaches: reverse and repost, reverse differences, change the original. If you need to know why the original was changed, in a traditional DB you need an additional audit trail. Implementers can neglect to implement a n audit table. With QLDB, there is no risk that the implementers will choose to update the original deposit, because the database is write-once.