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
|
|
|
T3 T4
|
|
|
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.
