ITPEC FE Subject A October 2025 Question 22

Transactions are executed without affecting each other — Isolation is the I of ACID and concerns concurrent transactions.

The four ACID properties each guarantee one thing:

• •Atomicity — a transaction is either completed in full or rolled back in full.
• •Consistency — a transaction takes the database from one valid state to another, so only valid data is written.
• •Isolation — concurrent transactions do not see each other's intermediate results, so the outcome is as if they ran one after another.
• •Durability — once committed, the changes survive failures.

Answer (d)

Why not others:

• •(a) — permanence after commit is Durability.
• •(b) — writing only valid data is Consistency.
• •(c) — all-or-nothing completion is Atomicity.

Key rule: Match each ACID letter to its single guarantee: all-or-nothing (A), valid states (C), no interference between concurrent transactions (I), survives failure (D).

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