DBMS Interview questions1

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Ques 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.

Ques Describe the three levels of data abstraction?

Ans
The are three levels of abstraction:

1) Physical level: The lowest level of abstraction describes how data are stored.

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

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



Ques What is the basic difference between DBMS and RDBM...
Answer
The difference in RDBMS and DBMS does not lie in the way tables and data are related to each other (ie. the Foreign Key relationship). dBase and MS Access are DBMS's which have foreign key relationships implemented.

RDBMS is based on the concepts of Relational Set Theory in mathematics and hence the name Relational Database Management System. They implement the project restrict union intersect difference product divide and join in the queries. DBMS's on the other hand supports two or more but not all of the concepts.

Q Disadvantage in File Processing System?

ANSWER:

? Data redundancy & inconsistency.
? Difficult in accessing data.
? Data isolation.
? Data integrity.
? Concurrent access is not possible.
? Security Problems. .


Ques What is a Database system?

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

Q What is the foreign key

Ans
A foreign key is a field in a table that refers to parent records in another table. The references are represented by the primary key values of the corresponding parent records. A foreign key field is the same data type as the primary key field of the referenced table. Usually, a foreign key field is named the same as the primary key field of the parent table. This very beneficial convention is called key migration in data modeling terminology. Child table foreign key references to parent table primary keys embody database relationships.


Ques Define the "integrity rules"

ANs:
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


Ques What is extension and intension?

ANS:
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.


QUES What is System R? What are its two major subsystems?

ANS
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

1) Research Storage

2) System Relational Data System.


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

ANS :
Unlike Relational systems in System R

1) Domains are not supported

2) Enforcement of candidate key uniqueness is optional

3) Enforcement of entity integrity is optional

4) Referential integrity is not enforced

QUE 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:
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

QUES What is a view? How it is related to data independence?

ANS
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence. .

QUES What is Data Model?

ANS
A collection of conceptual tools for describing data, data relationships data semantics and constraints.











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