Database Management Systems (2130703)

BE | Semester-3   Summer-2018 | 05/23/2018

Q5) (b)

Elaborate Normalization. Explain any two normal forms with suitable example(s).

Normalization

Normalization is a process of organizing the data in database to avoid data redundancy, insertion anomaly, update anomaly & deletion anomaly. Let’s discuss about anomalies first then we will discuss normal forms with examples.

First normal form (1NF)

As per the rule of first normal form, an attribute (column) of a table cannot hold multiple values. It should hold only atomic values.
Example: Suppose a company wants to store the names and contact details of its employees. It creates a table that looks like this:
emp_id emp_name emp_address emp_mobile
101 Herchel New Delhi 8912312390
102 Jon Kanpur 8812121212, 9900012222
103 Ron Chennai 7778881212
104 Lester Bangalore 9990000123, 8123450987
Two employees (Jon & Lester) are having two mobile numbers so the company stored them in the same field as you can see in the table above.
This table is not in 1NF as the rule says “each attribute of a table must have atomic (single) values”, the emp_mobile values for employees Jon & Lester violates that rule.
To make the table complies with 1NF we should have the data like this:
emp_id emp_name emp_address emp_mobile
101 Herschel New Delhi 8912312390
102 Jon Kanpur 8812121212
102 Jon Kanpur 9900012222
103 Ron Chennai 7778881212
104 Lester Bangalore 9990000123
104 Lester Bangalore 8123450987

Second normal form (2NF)

A table is said to be in 2NF if both the following conditions hold:
  • Table is in 1NF (First normal form)
  • No non-prime attribute is dependent on the proper subset of any candidate key of table.
An attribute that is not part of any candidate key is known as non-prime attribute.
Example: Suppose a school wants to store the data of teachers and the subjects they teach. They create a table that looks like this: Since a teacher can teach more than one subjects, the table can have multiple rows for a same teacher.
teacher_id subject teacher_age
111 Maths 38
111 Physcis 38
222 Biology 38
333 Physics 40
333 Chemistry 40
Candidate Keys: {teacher_id, subject}
Non prime attribute: teacher_age
The table is in 1 NF because each attribute has atomic values. However, it is not in 2NF because non prime attribute teacher_age is dependent on teacher_id alone which is a proper subset of candidate key. This violates the rule for 2NF as the rule says “no non-prime attribute is dependent on the proper subset of any candidate key of the table”.
To make the table complies with 2NF we can break it in two tables like this:
teacher_details table:
teacher_id teacher_age
111 38
222 38
333 40
teacher_subject table:
teacher_id subject
111 Maths
111 Physics
222 Biology
333 Physics
333 Chemistry
Now the tables comply with Second normal form (2NF).