To Know about the basic of DBMS......

QUESTION :What is database?

ANSWER:

A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.

QUESTION :What is DBMS?

ANSWER:

1. Redundancy is controlled.
2. Unauthorised access is restricted.
3. Providing multiple user interfaces.
4. Enforcing integrity constraints.
5. Providing backup and recovery.

QUESTION :What is a Database system?

ANSWER:

The database and DBMS software together is called as Database system.

QUESTION :Disadvantage in File Processing System?

ANSWER:

1. Data redundancy & inconsistency.
2.Difficult in accessing data.
3. Data isolation.
4.Data integrity.
5.Concurrent access is not possible.
6. Security Problems. .

QUESTION :Describe the three levels of data abstraction?

ANSWER:

The are three levels of abstraction:
Physical level: The lowest level of abstraction describes how data are stored.

Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

View level: The highest level of abstraction describes only part of entire database.

QUESTION :Define the "integrity rules"?

ANSWER:

There are two Integrity rules.

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

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

QUESTION :What is extension and intension?

ANSWER:

Extension -It is the number of tuples present in a table at any instance. This is time dependent.
Intension - It is a constant value that gives the name, structure of table and the constraints laid on it.

QUESTION :What is System R? What are its two major subsystems?

ANSWER:

System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center . It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.

Its two subsystems are

*Research Storage.
* System Relational Data System.

QUESTION :How is the data structure of System R different from the relational structure?

ANSWER:

Unlike Relational systems in System R
* Domains are not supported
* Enforcement of candidate key uniqueness is optional
* Enforcement of entity integrity is optional
* Referential integrity is not enforced

QUESTION :What is Data Independence?

ANSWER:

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:

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

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

NOTE: Logical Data Independence is more difficult to achieve