Thus, because of the failure, the state of the system no longer reflects
a real state of the world that the database is supposed to capture.
We term such a state an inconsistent state. We must ensure that such inconsistencies
are not visible in a database system. Note, however, that the system must at
some point be in an inconsistent state. Even if transaction Ti is executed to
completion, there exists a point at which the value of account Ais $950 and the
value of account B is $2000, which is clearly an inconsistent state. This state,
however, is eventually replaced by the consistent state where the value of
account A is $950, and the value of account B is $2050. Thus, if the transaction
never started orwas guaranteed to complete, such an inconsistent statewould
not be visible except during the execution of the transaction. That is the reason
for the atomicity requirement: If the atomicity property is present, all actions
of the transaction are reflected in the database, or none are.