What is the need for normalization? Explain 2nd and 3rd normal form with example.
Consider the following relation:
EMP_PROJ { SSn, Pnumber, Hours, Ename, Pname, Plocation}
Assume { SSn, Pnumber} as primary key.
The dependencies are {SSn, Pnumber}→ Hours; SSn →Ename; Pnumber → {Pname, Plocation}.
Normalize the above relation into 2NF.
Objectives of Normalization
Second normal form (2NF)
A table is said to be in 2NF if both the following conditions hold:
An attribute that is not part of any candidate key is known as non-prime attribute.
Consider the Table1 in First Normal Form, while the candidate key is {Student, Subject}, Age of Student only depends on Student column, Student → Age, which is incorrect as per Second Normal Form. To achieve second normal form, it would be helpful to split out the subjects into an independent table, and match them up using the student names as foreign keys.
Table1
Student |
Age |
Subject |
Adam |
15 |
Biology |
Adam |
15 |
Maths |
Alex |
14 |
Maths |
Stuart |
17 |
Maths |
After splitting, there are two tables,
Table 1:
Student |
Age |
Adam |
15 |
Alex |
14 |
Stuart |
17 |
Table 2
Student |
Subject |
Adam |
Biology |
Adam |
Maths |
Alex |
Maths |
Stuart |
Maths |
Third Normal Form (3NF)
Third Normal form applies that every non-prime attribute of table must be dependent on primary key, or we can say that, there should not be the case that a non-prime attribute is determined by another non-prime attribute. So this transitive functional dependency should be removed from the table and also the table must be in Second Normal form.
In this table Student_id is Primary key, but street, city and state depends upon Zip. The dependency between zip and other fields is called transitive dependency. Hence to apply 3NF, we need to move the street, city and state to new table, with Zip as primary key.
New Student_Detail Table:
Student_id |
Student_name |
DOB |
Zip |
Address Table:
Zip |
Street |
city |
state |
After removing the partial dependencies EMP_PROJ table, there will be three tables,
as below,
State the advantages of using database system over file-based information system.
State the steps involved in query processing. Why is the query optimization needed?
What is tree traversal?
Write the recursive algorithm to find x^ n.
Write short notes: B tree