As the name suggests, the database management system consists of two parts. They are:
- Database and
- 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:
| Roll |
Name
|
Age
|
1
|
ABC
|
19
|
2
|
DEF
|
22
|
3
|
XYZ
|
28
|
| Roll |
Address
|
1
|
KOL
|
2
|
DEL
|
3
|
MUM
|
| 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 andHostel attributes are in different tables.
In a database, data is organized strictly in row and column format. The rows are calledTuple 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.