DP-900 Describe core data concepts Practice Question
This DP-900 practice question tests your understanding of describe core data concepts. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
In a banking application, a transaction transfers $100 from Account A to Account B. The system deducts $100 from Account A successfully, but due to a network error, the credit to Account B fails. The application rolls back the deduction from Account A, ensuring that neither account is affected. Which ACID property is being enforced?
Atomicity ensures the transaction is all-or-nothing; if any part fails, the entire transaction is rolled back, as seen in this example.
B
Consistency
Why wrong: Consistency ensures that a transaction brings the database from one valid state to another, but it does not directly handle partial failure rollback.
C
Isolation
Why wrong: Isolation prevents concurrent transactions from interfering with each other, but it does not address the rollback of a failed transaction.
D
Durability
Why wrong: Durability ensures that once a transaction is committed, it persists even in a system failure, but it does not handle rollbacks.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Atomicity
Atomicity ensures that a transaction is treated as a single, indivisible unit of work. In this scenario, the deduction from Account A and the credit to Account B must both succeed or both fail entirely. When the credit to Account B fails, the system rolls back the deduction from Account A, preserving the all-or-nothing nature of the transaction. This is the core behavior of atomicity in ACID-compliant database systems like Azure SQL Database or SQL Server.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 ensures the transaction is all-or-nothing; if any part fails, the entire transaction is rolled back, as seen in this example.
Related concept
Read the scenario before looking for a memorised answer.
✗
Consistency
Why it's wrong here
Consistency ensures that a transaction brings the database from one valid state to another, but it does not directly handle partial failure rollback.
✗
Isolation
Why it's wrong here
Isolation prevents concurrent transactions from interfering with each other, but it does not address the rollback of a failed transaction.
✗
Durability
Why it's wrong here
Durability ensures that once a transaction is committed, it persists even in a system failure, but it does not handle rollbacks.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the rollback action with consistency, because both involve maintaining a correct state, but atomicity specifically governs the all-or-nothing completion of the transaction itself, not the validity of the data rules.
Detailed technical explanation
How to think about this question
Under the hood, atomicity is typically implemented using a transaction log (e.g., SQL Server's transaction log or Azure Cosmos DB's write-ahead log). Before any data modification, the 'before' image is written to the log, allowing a rollback to undo changes by replaying the log in reverse. In distributed systems like Azure SQL Database, atomicity across multiple nodes may rely on two-phase commit (2PC) or distributed transaction coordinators (e.g., MSDTC) to ensure all participants agree on the outcome.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-900 question in full detail.
Describe core data concepts — This question tests Describe core data concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Atomicity — Atomicity ensures that a transaction is treated as a single, indivisible unit of work. In this scenario, the deduction from Account A and the credit to Account B must both succeed or both fail entirely. When the credit to Account B fails, the system rolls back the deduction from Account A, preserving the all-or-nothing nature of the transaction. This is the core behavior of atomicity in ACID-compliant database systems like Azure SQL Database or SQL Server.
What should I do if I get this DP-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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