1.Which of the following plays an important role in representing informa-tion about the real world in a database? Explain brie?y.
1. The data de?nition language.
2. The data manipulation language.
3. The bu?er manager.
4. The data model.
2.Answer the following questions:
1. What is a transaction?
2. Why does a DBMS interleave the actions of di?erent transactions instead of exe-cuting transactions one after the other?
3. What must a user guarantee with respect to a transaction and database consis-tency? What should a DBMS guarantee with respect to concurrent execution of several transactions and database consistency?
4. Explain the strict two-phase locking protocol.
5. What is the WAL property, and why is it important?