What makes a sequence of database operations a transaction
The correct answer and explanation is:
Correct Answer:
A sequence of database operations is considered a transaction if it satisfies the ACID properties: Atomicity, Consistency, Isolation, and Durability.
Explanation:
A transaction in database systems is a logical unit of work that contains one or more operations. These operations can include insertions, deletions, updates, or retrievals. What makes a sequence of these operations a transaction is the guarantee that they will behave according to the ACID principles:
- Atomicity means the transaction is indivisible. All operations in the transaction must either be fully completed or fully rolled back. If one part fails, the entire transaction fails and the database remains unchanged.
- Consistency ensures that a transaction takes the database from one valid state to another. The integrity constraints of the database must not be violated at any point. This protects the validity of the data before and after the transaction.
- Isolation ensures that transactions are executed independently. Even when multiple transactions are processed simultaneously, each must behave as if it is the only one running. This prevents problems such as dirty reads or lost updates.
- Durability guarantees that once a transaction has been committed, its effects are permanent, even in the case of a system crash or power failure. The changes made to the database survive system restarts.
A simple example is a bank money transfer from one account to another. The transaction involves debiting one account and crediting another. If either step fails, the transaction is rolled back to avoid inconsistencies. Without atomicity and consistency, money could disappear or duplicate. Isolation ensures no interference from other transfers, and durability secures the result after the transfer completes.
By satisfying these ACID properties, a sequence of database operations is reliably treated as a transaction. This enables robust, reliable, and predictable behavior in database management systems.