Example of Fund Transfer (Cont.)
Example of Fund Transfer (Cont.)
Consistency requirement in above example:
the sum of A and B is unchanged by the execution of the
transaction
In general, consistency requirements include
Explicitly specified integrity constraints such as primary keys and
foreign keys
Implicit integrity constraints
–
e.g. sum of balances of all accounts, minus sum of loan
amounts must equal value of cash-in-hand
A transaction must see a consistent database.
When the transaction completes successfully the database must be
consistent
Erroneous transaction logic can lead to inconsistency
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