Consider the following transaction involving two bank accounts $x$ and $y$ . read(x) ; x := x - 50; write(x) ; read(y) ; y:= y + 50; write(y) The constraint that the sum of the accounts $x$ and $y$ should remain constant is that of

In database transaction processing, the ACID properties are:

• Atomicity: Ensures all operations within a transaction are executed completely or none at all.

• Consistency: Ensures that the execution of a transaction takes the database from one valid (consistent) state to another, satisfying all integrity constraints (such as preserving total account balances: $x + y = \text{constant}$ before and after transfer).

• Isolation: Ensures concurrent execution of transactions leaves the database in the same state as if they were executed sequentially.

• Durability: Ensures that committed updates persist even in the event of a system crash.

The requirement that $x + y$ remains constant is an integrity constraint, which relates directly to the Consistency property.

Therefore, B is the correct option.