6.18- Third normal form In DBMS With Easy Example | 3nf in dbms | Normalization in dbms

6.18- Third normal form In DBMS With Easy Example | 3nf in dbms | Normalization in dbms

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Relational Database Design- Functional Dependencies And Normalization


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Third Normal Form (3NF)
A relation is in Third Normal Form if it is in 2NF and non-primary key attributes must
be non-transitively dependent upon primary key attributes.
In other words a relation is in 3NF if it is in 2NF and having no transitive dependency.
Consider the relation Student as shown in Figure 6.12(a).
Student
RollNo. Name Semester Hostel
1 Lalit 1 H1
2 Gaurav 2 H2
3 Vishal 1 H1
4 Neha 4 H4
5 John 3 H3
(a)
Functional Dependency and Normalisation 219
RollNo
Name
Semester
Hostel
(b)

FIGURE 6.12. Student relation.
The Primary Key is (RollNo.). The condition is different Hostel is allotted for different
semester. Student relation is in 2NF but still contains anomalies.
1. Deletion anomaly : If you want to delete student Gaurav. You loose information
about Hostel H2 because he is the only student staying in hostel H2.
2. Insertion anomaly : If you want to add a new Hostel H8 and this is not allotted
to any student. You cannot add this information.
3. Updation anomaly : If you want to change hostel of all students of first semester.
You have to search all the students of first semester and update them individually
otherwise it causes inconsistency.
The solution of this problem is to divide relation Student into two relations Student(RollNo.
Name, Semester) and Hostels(Semester, Hostel) Notes Link:
http://www.tutorialsspace.com/Downloa...