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Database Management System, What is a Database?, Data, Record

 

Introduction to Database Management System

As the name suggests, the database management system consists of two parts.  They are:

1.      Database and

2.      Management System

 

What is a Database?

To find out what database is, we have to start from data, which is the basic building block of any DBMS.

 

Data: Facts, figures, statistics etc. having no particular meaning (e.g. 1, ABC, 19 etc).

Record: Collection of related data items, e.g. in the above example the three data items had no meaning. But if we organize them in the following way, then they collectively represent meaningful information.




Roll

Name

Age

1

ABC

19

 Table or Relation: Collection of related records.


Roll

Name

Age

1

ABC

19

2

DEF

22

3

XYZ

28


 The columns of this relation are called Fields, Attributes or Domains. The rows are called Tuples or Records.

Database
: Collection of related relations. Consider the following collection of tables:

       T1                                                                          T2

 

Roll

Name

Age

1

ABC

19

2

DEF

22

3

XYZ

28

 

Roll

Address

1

KOL

2

DEL

3

MUM

 

       T3                                                                          T4  

 

 

Roll

Year

1

I

2

II

3

I

 

 

Year

Hostel

I

 

H1

 

II

H2

 

We now have a collection of 4 tables. They can be called a “related collection” because we can clearly find out that there are some common attributes existing in a selected pair of tables. Because  of these common attributes we may combine the data of two or more tables together to find out the complete details of a student. Questions like “Which hostel does the youngest student live in?” can be answered now, although Age and Hostel attributes are in different tables.

 

A database in a DBMS could be viewed by lots of different people with different responsibilities.

 

 


 

Figure 1.1: Empolyees are accessing Data through DBMS

 

For example, within a company there are different departments, as well as customers, who each need to see different kinds of data. Each employee in the company will have different levels of access to the database with their own customized front-end application.

In a database, data is organized strictly in row and column format. The rows are called Tuple or Record. The data items within one row may belong to different data types. On the other hand, the columns are often called Domain or Attribute. All the data items within a single attribute are of the same data type.

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