4. When a foreign key column is created without a corresponding foreign key constraint, we have created a "casual relationship" between the two tables.
6. Two transactions that run concurrently and generate results that are consistent with the results that would have occurred if they had run separately are referred to as serializable transactions.
8. A phantom read occurs when a transaction rereads data it has previously read and finds modifications or deletions caused by a committed transaction.
9. A transaction is a series of actions to be taken on the database so that either all of them are performed successfully or none of them are performed at all.