DP-900 Describe core data concepts Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Atomicity

  Why this is correct

  Atomicity guarantees that a transaction's operations are executed as an all-or-nothing unit. If the $100 debit from one account succeeds but the $100 credit to another account fails, atomicity requires the entire transaction to be rolled back, returning the database to its pre-transaction state. Without atomicity, a partial transfer would leave the bank with inconsistent balances and potential lost or duplicated funds.

• ✗

  Consistency

  Why it's wrong here

  Consistency ensures that a database moves from one valid state to another, respecting all defined constraints such as foreign keys and check constraints, like preventing negative account balances. It describes the correctness of the entire data set before and after a transaction, but it does not govern how the database handles a partial failure inside a transaction. If the credit leg fails, consistency alone does not mandate reversing the debit; it only says the final state must be valid, and atomicity is the property that actually enforces the rollback.

  When this WOULD be correct

  In a scenario where a transaction deducts $100 from Account A and credits $100 to Account B, but the credit violates a constraint (e.g., Account B's balance exceeds a limit), causing the transaction to fail and roll back. The question would ask which property ensures the database remains in a valid state before and after the transaction.

• ✗

  Isolation

  Why it's wrong here

  Isolation governs how the database handles concurrent transactions by ensuring that one transaction’s intermediate results are not visible to others until it commits, preventing phenomena like dirty reads or lost updates. It does not provide any mechanism to undo the changes of a failed transaction; a failed transaction's partial writes must be reverted by the atomicity property. In this transfer example, isolation would keep the debit hidden from other transactions during processing, but it would not automatically reverse that debit when the credit operation fails.

  When this WOULD be correct

  A question where two transactions run simultaneously, e.g., Transaction 1 reads Account A balance while Transaction 2 transfers money from Account A to B, and the system prevents Transaction 1 from seeing intermediate states (e.g., uncommitted debit). Isolation would be the property ensuring each transaction appears to execute in isolation.

• ✗

  Durability

  Why it's wrong here

  Durability ensures that once a transaction is committed, its changes are permanently persisted in non-volatile storage and survive crashes or power failures. However, durability does not address what happens when an in-progress transaction fails or is aborted; it only protects successfully committed data. In this transfer scenario, durability would not roll back the debit if the credit operation fails — that rollback action is specifically the domain of atomicity.

  When this WOULD be correct

  Durability would be correct if the question described a transaction that successfully completed (e.g., both debit and credit were committed) and then the system crashed, but upon recovery the changes were still present.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The DP-900 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official DP-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

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