Database Reference
In-Depth Information
In the above figure we have five columns in student table. Let d
1
represents the set of all
Registration No, d
2
is set of name, d
3
is set of semester, d
4
is set of Branch and d
5
is set of
cities
So the table Student can be represented as :
d
1
x d
2
x d
3
x d
4
x d
5
Example 1:
The possible domain definitions for the attributes person-name, date-of-birth,
and city might be:
PERSON-NAMES = {Ajit Kumar, Aman, Ram Gopal , Akash, Anjali, Balraj} CITY = {
Hoshiarpur, Jalandhar, Ludhiana, Patiala, Bathinda}
DATE-OF-BIRTH = {a string in dd-mm-yyyy format, such that: 03-02-1940 dd, mm,
yyyy represent day, month year}
To make the distinction between the attributes and their corresponding domains, we are
using small letters for the names of the attributes and capital letters for the domains. An
empty set {} is a member of any of these domains.
4.3 TABLE
According to the relational model, data in a relational database is stored in relations, which
are perceived by the user as tables. Each relation is composed of tuples (records) and at-
tributes (fields). A table that stores data used to supply information is called a
data table
,
and it is the most common type of table in a relational database. Data in this type of table
is dynamic because you can manipulate it (modify, delete, and so forth) and process it into
information in some form or fashion.
4.4 FIELD
A field (also called an attribute in theory of relational database) is the smallest structure in
the database. It shows a characteristic of the subject of the table to which it belongs. Fields
are the structures that actually hold data. The data in these fields can then be retrieved and
presented as useful information. The importance of fields cannot be ignored. Every field
contains one and only one value, and its name will identify the type of value it store. If
you see fields with names such as RollNo, Name, City, State, And Zipcode, you can easily
imagine exactly what type of values move into each field.
