Third Normal Form (3NF) in DBMS Theory - Mini Project: Build & Apply

Understanding Third Normal Form (3NF) in Databases

📖 Scenario: You are designing a simple database for a small bookstore. The database should store information about books, authors, and publishers. To keep the data organized and avoid redundancy, you want to apply the Third Normal Form (3NF) rules.

🎯 Goal: Build a step-by-step example that shows how to organize a bookstore database table into Third Normal Form (3NF) by creating tables and defining relationships.

📋 What You'll Learn

Create an initial table with book details including author and publisher information

Add a configuration step to identify functional dependencies

Apply the core logic of decomposing the table into multiple tables to achieve 3NF

Complete the design by defining primary keys and foreign keys for the tables

💡 Why This Matters

🌍 Real World

Database designers use 3NF to organize data efficiently, avoid duplication, and maintain consistency in applications like bookstores, libraries, and inventory systems.

💼 Career

Understanding 3NF is essential for roles like database administrators, data analysts, and software developers to design scalable and maintainable databases.

1

Create the initial bookstore table

Create a table called Bookstore with columns BookID, BookTitle, AuthorName, AuthorEmail, PublisherName, and PublisherAddress.

DBMS Theory

# Create the Bookstore table with the specified columns
# Your code here

Hint

Define a table with all columns in one place to show initial data structure before normalization.

2

Identify functional dependencies

Create a comment that lists the functional dependencies: BookID determines BookTitle, AuthorName, and PublisherName. Also, AuthorName determines AuthorEmail, and PublisherName determines PublisherAddress.

DBMS Theory

CREATE TABLE Bookstore (
  BookID INT,
  BookTitle VARCHAR(100),
  AuthorName VARCHAR(100),
  AuthorEmail VARCHAR(100),
  PublisherName VARCHAR(100),
  PublisherAddress VARCHAR(200)
);
-- List functional dependencies here
# Your code here

Hint

Write the functional dependencies as comments to understand which columns depend on others.

3

Decompose the table to achieve 3NF

Create three tables: Books with BookID, BookTitle, AuthorName, and PublisherName; Authors with AuthorName and AuthorEmail; and Publishers with PublisherName and PublisherAddress.

DBMS Theory

-- Create Books table
# Your code here

Hint

Split the original table into three tables so that each non-key attribute depends only on the key.

4

Define primary keys and foreign keys

Add foreign key constraints: in Books, set AuthorName as a foreign key referencing Authors(AuthorName) and PublisherName as a foreign key referencing Publishers(PublisherName).

DBMS Theory

ALTER TABLE Books
-- Add foreign key constraints here
# Your code here

Hint

Use FOREIGN KEY clauses inside the Books table to link to Authors and Publishers.

Practice

1. What is the main goal of the Third Normal Form (3NF) in database design?

easy

A. To ensure no non-key column depends on another non-key column

B. To remove all duplicate rows from a table

C. To combine multiple tables into one

D. To allow NULL values in all columns

Solution

1. Step 1: Understand 3NF definition

   3NF requires that every non-key column depends only on the primary key, not on other non-key columns.

2. Step 2: Compare options with 3NF goal

   Only To ensure no non-key column depends on another non-key column correctly states this goal. Other options describe different concepts.

3. Final Answer:

   To ensure no non-key column depends on another non-key column -> Option A

4. Quick Check:

   3NF = No transitive dependency [OK]

Hint: 3NF removes transitive dependencies between non-key columns [OK]

Common Mistakes:

• Confusing 3NF with removing duplicates
• Thinking 3NF merges tables
• Believing 3NF allows NULLs everywhere

2. Which of the following functional dependencies violates the Third Normal Form (3NF)?

easy

A. PrimaryKey -> NonKeyColumn

B. NonKeyColumn1 -> NonKeyColumn2

C. PrimaryKey -> CompositeKey

D. PrimaryKey -> ForeignKey

Solution

1. Step 1: Identify 3NF violation

   3NF disallows non-key columns determining other non-key columns (transitive dependency).

2. Step 2: Analyze each dependency

   NonKeyColumn1 -> NonKeyColumn2 shows a non-key column determining another non-key column, violating 3NF.

3. Final Answer:

   NonKeyColumn1 -> NonKeyColumn2 -> Option B

4. Quick Check:

   Transitive dependency = 3NF violation [OK]

Hint: Watch for non-key to non-key dependencies breaking 3NF [OK]

Common Mistakes:

• Assuming all dependencies from primary key violate 3NF
• Confusing foreign keys with functional dependencies
• Ignoring transitive dependencies

3. Consider a table with columns StudentID (primary key), AdvisorName, and AdvisorOffice. If AdvisorName determines AdvisorOffice, which of the following is true about this table regarding 3NF?

medium

A. The table is in 3NF because StudentID is the primary key

B. The table violates 3NF because AdvisorOffice depends on StudentID

C. The table is in 3NF because AdvisorOffice depends on AdvisorName

D. The table violates 3NF due to transitive dependency

Solution

1. Step 1: Identify dependencies

   StudentID -> AdvisorName and AdvisorName -> AdvisorOffice shows a transitive dependency.

2. Step 2: Check 3NF rules

   3NF disallows non-key columns (AdvisorName) determining other non-key columns (AdvisorOffice).

3. Final Answer:

   The table violates 3NF due to transitive dependency -> Option D

4. Quick Check:

   Transitive dependency breaks 3NF [OK]

Hint: Check if non-key columns determine others to spot 3NF violation [OK]

Common Mistakes:

• Thinking primary key alone ensures 3NF
• Ignoring transitive dependencies
• Confusing direct and transitive dependencies

4. A table has columns OrderID (primary key), CustomerName, and CustomerCity. The dependency CustomerName -> CustomerCity exists. What is the problem with this table in terms of 3NF, and how can it be fixed?

medium

A. Violates 3NF; fix by splitting into two tables separating customer info

B. No problem; table is already in 3NF

C. Violates 3NF; fix by adding CustomerCity to primary key

D. No problem; just rename columns

Solution

1. Step 1: Identify 3NF violation

   CustomerName -> CustomerCity is a transitive dependency violating 3NF.

2. Step 2: Fix violation by normalization

   Split table into Orders and Customers tables to separate customer details.

3. Final Answer:

   Violates 3NF; fix by splitting into two tables separating customer info -> Option A

4. Quick Check:

   Split tables to remove transitive dependencies [OK]

Hint: Split tables to remove non-key to non-key dependencies [OK]

Common Mistakes:

• Adding columns to primary key incorrectly
• Ignoring transitive dependencies
• Thinking renaming fixes normalization

5. You have a table with columns EmployeeID (primary key), DepartmentID, DepartmentName, and ManagerID. DepartmentID determines DepartmentName and ManagerID. How should you redesign the table to achieve Third Normal Form (3NF)?

hard

A. Keep all columns in one table because EmployeeID is primary key

B. Add DepartmentName and ManagerID to EmployeeID primary key

C. Create two tables: one for Employees and one for Departments with DepartmentID as key

D. Remove ManagerID column to fix 3NF

Solution

1. Step 1: Identify transitive dependencies

   DepartmentID -> DepartmentName and ManagerID means non-key columns depend on another non-key column.

2. Step 2: Normalize by splitting tables

   Create separate Department table with DepartmentID as key to remove transitive dependencies.

3. Final Answer:

   Create two tables: one for Employees and one for Departments with DepartmentID as key -> Option C

4. Quick Check:

   Split tables to remove transitive dependencies [OK]

Hint: Separate dependent columns into new table keyed by determinant [OK]

Common Mistakes:

• Keeping all columns in one table ignoring transitive dependency
• Adding columns to primary key unnecessarily
• Removing important columns instead of normalizing