DBMS Questions

1. What is DBMS?

It is a collection of programs that helps the user to create and maintain a database.

2. What is database system?

 It is a combination of database and DBMS software.

3. Merits of DBMS:

 Control redundancy.

Restrict unauthorized access 

Allow multiple user interfaces

Enforce integrity constraints

Provide backup and recovery.

4.What are the levels of  Levels of abstraction?

 Physical level: The lowest level abstraction that describes how data is stored.

Logical level: Middle level of abstraction Which describes what data are stored and what is the relationship among the data

View level: Highest level of abstraction that describes only part of the database.

5. Two types of integrity rules

 Entity Integrity: Primary key cannot be NULL

Referential Integrity: Foreign key can either be NULL or should be a primary key of another relation.

6. What is the difference between physical data independence and logical data independence?

 Physical data independence: Modification in physical level should not affect logical level

Logical data independence: Modification in logical level should affect view level.

7. What is SDL?

 SDL means Storage Definition Language

It specifies internal schema and also mapping between two schemas.

8. What is a DML compiler?

 It helps to translate DML statements in the query language into low level instruction that is understood by the query evaluation engine.

9. What is relational algebra?

It is a procedural query language. 

It is a set of operations that take one or two relations as input and produce a new relation.

10. What is transparent DBMS?

 It is the DBMS that keeps its physical structure hidden from user.

11. If a relation is in 2NF, then

Every non-prime attribute is fully functionally dependent on each relation key.

12. The data type created by data abstraction process is called as

Class

13. An entity instance is a single occurence of 

An entity type

14. A relation which is in BCNF is always in which NF

3NF

15. 2-phase locking protocol suffers from

Deadlocks

16. Time stamp protocol suffers from

Frequent aborts, cascading rollbacks

17. In generalization, the difference between members of an entity is

Maximized.

18. Some of the commonly used Aggregate functions are

SUM, AVG, COUNT

19. A locked file can be 

* Modified by users with correct password

* Used to hide sensitive information.

20. A recursive foreign key 

References its own relation.