Frequently Asked Tough Database DBMS job interview Questions Answers & Solve Paper

 Q. Explain the meaning of the expression ACID transaction.

ACID means Atomic, Consistency, Isolation, Durability, so when any transaction happen it should be Atomic that is it should either be complete or fully incomplete. There should not be anything like Semi complete. The Database State should remain consistent after the completion of the transaction. If there are more than one Transaction then the transaction should be scheduled in such a fashion that they remain in Isolation of one another. Durability means that Once a transaction commits, its effects will persist even if there are system failures.

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Q. Explain the difference between an explicit and an implicit lock.

Explicit Lock :- Lock is explicitly requested for a record or table.

Implicit Lock :- Lock is implied but is not acquired.

Q. Explain how a database could be recovered via reprocessing. Why is this generally not feasible?

If we reprocess the transaction then the database can be made to come to a state where the database is consistent and so reprocessing the log can recover the database. Reprocessing is not very feasible for a very simple reason that its very costly from time point of view and requires lots of rework and many transaction are even rollback giving more and more rework.

Q. Define rollback and roll forward.

Rollback :- Undoing the changes made by a transaction before it commits or to cancel any changes to a database made during the current transaction

Roll Forward :- Re-doing the changes made by a transaction after it commits or to overwrite the changed clue again to ensure consistency

Q. What are the advantages of DBMS?

1. Redundancy is controlled.

2. Unauthorized access is restricted.

3. Providing multiple user interfaces.

4. Enforcing integrity constraints.

5. Providing backup and recovery.

Q. Define the "integrity rules"?

There are two Integrity rules. 

1. Entity Integrity: States that "Primary key cannot have NULL value"

2. Referential Integrity: States that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.

Q. What is Data Independence?

Data independence means that "the application is independent of the storage structure and access strategy of data". In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.

Two types of Data Independence: 

1. Physical Data Independence: Modification in physical level should not affect the logical level.

2. Logical Data Independence: Modification in logical level should affect the view level.

NOTE: Logical Data Independence is more difficult to achieve