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.

• ✗

  Consistency

  Why it's wrong here

  Consistency ensures that a transaction moves the database from one valid state to another by enforcing all integrity constraints, such as foreign keys, unique indexes, check constraints, and custom business rules. In a fund transfer, consistency could verify that the sum of all account balances is preserved or that a negative balance is not allowed, but it does not specify what happens when a statement fails halfway through. A database can be consistent before and after a transaction yet still leave partial writes if the transaction is not atomic. Thus, consistency is a state-oriented guarantee, whereas the question describes a process-oriented all-or-nothing guarantee.

  When this WOULD be correct

  A question that asks: 'A bank transfer ensures that the total balance across accounts remains the same before and after the transaction. Which ACID property does this guarantee?' would make Consistency correct, as it maintains database invariants.

• ✗

  Isolation

  Why it's wrong here

  Isolation governs how the database handles the temporary intermediate state of a transaction while it is running, specifically shielding it from concurrently executing transactions. In the fund-transfer scenario, isolation would prevent another transaction from reading the account balance in the brief window after the debit but before the credit, avoiding inconsistent observations. However, isolation does not guarantee that the transfer itself will be rolled back if something goes wrong; it only serializes or flags concurrent access. The scenario is about failure atomicity, not about interference between simultaneous operations.

  When this WOULD be correct

  A question where two transactions run simultaneously, e.g., one reading a balance while another updates it, and the system prevents dirty reads or lost updates. The correct answer would be Isolation.

• ✗

  Durability

  Why it's wrong here

  Durability is the ACID property that only comes into play after the transaction has been successfully committed, not during its execution. It promises that once the database acknowledges the completed fund transfer, the changes will survive subsequent crashes, power losses, or media failures because the log records have been flushed to stable storage. Durability does not enforce any rollback semantics or all-or-nothing rule; it assumes the transaction already succeeded. Therefore, it cannot explain the requirement that a failure during the transfer leaves no partial debit.

  When this WOULD be correct

  A question stating: 'After a fund transfer is successfully committed, the system crashes. The bank later confirms the transfer was recorded permanently. Which ACID property is demonstrated?'

• ✓

  Atomicity

  Why this is correct

  Atomicity is the ACID property that treats the entire fund transfer as a single, indivisible unit of work. The transfer requires two physical operations—a debit from the source account and a credit to the destination account—and atomicity guarantees that either both operations persist or neither does. If any step fails, the database management system rolls back the entire transaction, restoring all affected rows to their pre-transaction state. This all-or-nothing behavior directly matches the scenario's requirement that a partial deduction cannot be left behind.

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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