What is a transaction in a database system?

• A) A single SQL statement executed on the database.
• B) A logical unit of work that accesses and possibly modifies data.
• C) A physical unit of data storage on disk.
• D) A sequence of database operations performed by a user.

Which of the following is NOT an ACID property of transactions?

• A) Atomicity
• B) Consistency
• C) Isolation
• D) Durability

What is concurrency control in a database system?

• a) The process of managing simultaneous access to data by multiple users
• b) The technique of optimizing database performance
• c) The method of securing database access
• d) The process of backing up the database

What is a deadlock in a database system?

• a) A situation where two or more transactions are waiting for each other to release locks
• b) A state where the database system crashes
• c) A condition where a transaction is unable to commit due to a system error
• d) A situation where a transaction is waiting for a resource that is not available

Which concurrency control technique uses timestamps to order transactions?

• a) Two-phase locking
• b) Timestamp ordering
• c) Optimistic concurrency control
• d) Pessimistic concurrency control

What is the purpose of a lock in a database system?

• a) To prevent unauthorized access to data
• b) To improve database performance
• c) To control concurrent access to data
• d) To encrypt sensitive data

What is a shared lock?

• a) A lock that allows multiple transactions to read a data item but prevents any transaction from modifying it
• b) A lock that allows only one transaction to access a data item, either for reading or writing
• c) A lock that allows multiple transactions to modify a data item simultaneously
• d) A lock that prevents any transaction from accessing a data item

What is an exclusive lock?

• a) A lock that allows multiple transactions to read a data item but prevents any transaction from modifying it
• b) A lock that allows only one transaction to access a data item, either for reading or writing
• c) A lock that allows multiple transactions to modify a data item simultaneously
• d) A lock that prevents any transaction from accessing a data item

What is a phantom read?

• a) A situation where a transaction reads a data item multiple times and gets different values
• b) A situation where a transaction reads a data item that has been deleted by another transaction
• c) A situation where a transaction reads a data item that has not yet been committed by another transaction
• d) A situation where a transaction reads a data item that has been modified by another transaction after the first transaction has read it

What is a non-repeatable read?

• a) A situation where a transaction reads a data item multiple times and gets different values
• b) A situation where a transaction reads a data item that has been deleted by another transaction
• c) A situation where a transaction reads a data item that has not yet been committed by another transaction
• d) A situation where a transaction reads a data item that has been modified by another transaction after the first transaction has read it