Third Normal Form (3NF) in DBMS Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to define Third Normal Form (3NF).

DBMS Theory

A table is in Third Normal Form if it is in Second Normal Form and every non-prime attribute is [1] on the primary key.

Drag options to blanks, or click blank then click option'

Atransitively dependent

Bdirectly dependent

Cindependent

Dpartially dependent

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing transitive dependency with direct dependency.

Thinking partial dependency is allowed in 3NF.

Third Normal Form requires that all non-prime attributes depend directly on the primary key, not through another attribute.

2fill in blank

medium

Complete the sentence to identify a violation of 3NF.

DBMS Theory

If a non-prime attribute depends on another non-prime attribute, it causes a [1] dependency, violating 3NF.

Drag options to blanks, or click blank then click option'

Atransitive

Bpartial

Cdirect

Dfunctional

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up partial and transitive dependencies.

Assuming direct dependency causes 3NF violation.

Transitive dependency occurs when a non-prime attribute depends on another non-prime attribute, which violates 3NF.

3fill in blank

hard

Fix the error in the statement about 3NF.

DBMS Theory

3NF requires that every attribute is [1] on the whole primary key and no transitive dependencies exist.

Drag options to blanks, or click blank then click option'

Afully dependent

Bindependent

Ctransitively dependent

Dpartially dependent

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing partial dependency with full dependency.

Ignoring the removal of transitive dependencies.

3NF requires full functional dependency on the primary key and no transitive dependencies.

4fill in blank

hard

Fill both blanks to complete the 3NF condition.

DBMS Theory

A relation is in 3NF if it is in [1] and no non-prime attribute is [2] on another non-prime attribute.

Drag options to blanks, or click blank then click option'

A2NF

B1NF

Ctransitively dependent

Dpartially dependent

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 1NF instead of 2NF as the base.

Confusing partial dependency with transitive dependency.

3NF requires the relation to be in Second Normal Form and to have no transitive dependencies among non-prime attributes.

5fill in blank

hard

Fill all three blanks to describe 3NF requirements.

DBMS Theory

To be in 3NF, a table must be in [1], have no [2] dependencies, and every non-prime attribute must depend [3] on the primary key.

Drag options to blanks, or click blank then click option'

A2NF

Btransitive

Cdirectly

D1NF

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting 1NF instead of 2NF.

Mixing up transitive and partial dependencies.

Thinking non-prime attributes can depend indirectly.

3NF requires the table to be in Second Normal Form, have no transitive dependencies, and all non-prime attributes to depend directly on the primary key.

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