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Saturday, December 31, 2011

DBMS Introduction




What is DBMS?
Ans: The data base management system consists of a collection interrelated and persistent data are referred to as database. A set of application programs used to access, update and manage the data forms the DBMS. The goal of DBMS is to store data into database and retrieve data from database. It allows different user application programs to concurrently access the same database.

What is different level of data abstraction?
Ans : There are three levels of data abstraction.
Physical level: The lowest level of abstraction describes how the data are actually stored. At the physical level, complex low-level data structures are described in detail.

Logical level: The next-higher level of abstraction describes what data are stored in the database, and what relationship exists among those data. The entire database is thus described in terms of small number of relatively simple structure. The user of the logical level does not need to be aware of the complexity.

View level: A view level is a subset of database or it may contain virtual data that is derived from a table (database) files but is not explicitly stored.


What are the differences between DDL and DML?
Ans:
DDL
DML
DDL is used by database administrator to define schema.
DML is used by database user to manipulate data in a database.
DDL is used to specify the conceptual schema.
Perform insert, delete, update in database.
DDL’s are CREATE,ALTER,DROP,COMMENT,
RENAME etc.
DML’s are SELECT,INSERT,UPDATE,DELETE,
MERGE etc.

Mention advantages of DBMS over file-processing system.
Ans:
1.      A database management system coordinates both physical and logical access to the data, whereas a file processing system only coordinates the physical access.

2.      A database management system is designed to allow flexible access to data whereas a file-processing system is designed to allow predetermined access to data.

3.      A database management system (DBMS) is designed to coordinate multiple users accessing the same database at the same time whereas in file-processing system one program is allowed to access one data at a time. 


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