How do transaction isolation levels differ in database management systems?

Transaction isolation levels determine how much one transaction can see the changes made by other concurrent transactions. The main isolation levels in DBMS:

1. Read Uncommitted — a transaction can see changes made by other transactions even if they are not yet committed. Dirty reads are possible.

2. Read Committed — a transaction only sees changes that have been committed. Dirty reads are prevented, but non-repeatable reads can occur.

3. Repeatable Read — guarantees that repeated reads of the same data will yield the same result, preventing non-repeatable reads. However, phantom reads can occur when new rows appear in subsequent queries.

4. Serializable — the strictest level, transactions are executed as if they were sequential. It prevents phantom reads and provides full isolation but reduces concurrency.

Choosing an isolation level is a trade-off between data integrity and performance.