Explain what a database transaction is, define the ACID properties (Atomicity, Consistency, Isolation, Durability), and describe common transaction isolation levels: Read Uncommitted, Read Committed, Repeatable Read, and Serializable. For each isolation level, discuss: - Which anomalies it prevents or allows (e.g., dirty reads, non-repeatable reads, phantom reads). - A concrete example scenario illustrating those anomalies. - When you might choose that level in a real-world application (e.g., financial system vs. analytics system). Also explain how isolation relates to performance and concurrency in a database system.