Starting UNIT 4 – DBMS — clean BEFA style.

First, covering all 2 Marks Questions one-by-one:

1. What is normalization in database design?

 Normalization is the process of organizing data to remove redundancy and improve

data integrity.

 It divides large tables into smaller related tables.

📘 Example:
Instead of keeping Student and Course details in one table, we split them into two related
tables.

2. Define functional dependency with an example.

 Functional Dependency means one attribute depends on another.

📘 Example:
If RollNo → Name, it means RollNo uniquely decides Name.
(If you know RollNo, you can find Name.)

3. What is the purpose of normalization in database design?

 To eliminate data redundancy (repeated data).

 To maintain data consistency.

 To make the database efficient for updates, deletions, and insertions.

4. What is a lossless join decomposition?

 Lossless join means when you split a table into two or more tables and later join them,
you still get the original table back without losing any information.

📘 Example:
Splitting a Student table into (StudentID, Name) and (StudentID, Course) is lossless if StudentID
links them correctly.
5. What is Boyce-Codd Normal Form (BCNF)?

 A table is in BCNF if:

o It is in 3NF.

o For every functional dependency X → Y, X is a super key (unique identifier).

📘 Example:
If a table has StudentID → Name, and StudentID is unique, then it follows BCNF.

6. What is the difference between 3NF and BCNF?

3NF BCNF

Allows non-super key attributes if no partial dependency Only super key attributes allowed

Slightly less strict More strict (stronger form of 3NF)

📘 In simple words:
BCNF is a stricter version of 3NF.

7. What does it mean for a decomposition to be lossless?

 It means that after splitting a table into smaller tables, when we join them again, there
is no missing data or extra data.

 It keeps the database accurate.

8. How do functional dependencies affect normalization?

 Functional dependencies guide how tables should be split during normalization.

 They help identify repeating or unnecessary data that should be removed.

9. What is a composite key in the context of normalization?

 A composite key is a combination of two or more attributes that together uniquely

identify a record.
📘 Example:
(StudentID, CourseID) together can uniquely identify a student's enrollment.

10. Explain the concept of Multivalued Dependency (MVD).

 Multivalued dependency happens when one attribute independently depends on

another attribute.

📘 Example:

 Employee → Project

 Employee → Skill

Means employee's projects and skills are independent but both related to employee.

All 2 Marks of Unit 4 completed.

Now ready to immediately continue with Unit 4 – 10 Marks Questions one-by-one.

Proceeding to next: Q11 ✅

Continuing immediately with Unit 4 – 10 Marks Questions:

📘 11. Explain the Purpose of Normalization. Discuss Different Normal Forms (1NF, 2NF, and
3NF) with Examples 🎯

🧠 Purpose of Normalization

 Remove data redundancy (no repeated data).

 Avoid update, insertion, and deletion anomalies.

 Simplify database structure.

 Improve data integrity and consistency.

📘 Real-life example:
If a student’s phone number is stored multiple times in different tables, updating it everywhere
is risky. Normalization solves this by organizing data properly.
🔹 Different Normal Forms:

1. First Normal Form (1NF) 📄

 No multi-valued or repeating groups.

 Each field contains only atomic (single) values.

📘 Example:

Bad Table (Not in 1NF):

RollNo Name Subjects

1 John Math, Science

Good Table (1NF):

RollNo Name Subject

1 John Math

1 John Science

2. Second Normal Form (2NF) 📋

 Must be in 1NF.

 No partial dependency (non-prime attribute must depend on whole primary key).

📘 Example:

Bad Table:

StudentID CourseID CourseName

1 101 Math

Here, CourseName depends only on CourseID, not on StudentID and CourseID together.

Solution: Split into two tables:

 (StudentID, CourseID)

 (CourseID, CourseName)
3. Third Normal Form (3NF) 📄

 Must be in 2NF.

 No transitive dependency (non-prime attribute depending on another non-prime

attribute).

📘 Example:

Bad Table:

StudentID Name Department HODName

Here, HODName depends on Department, not on StudentID directly.

Solution: Split into:

 (StudentID, Name, Department)

 (Department, HODName)

📘 Quick Table Summary:

Normal Form Rule Example Fix

1NF Atomic values only No multivalued fields

2NF No partial dependency Attributes depend on full key

3NF No transitive dependency Attributes depend only on key

✅ Conclusion:

Normalization organizes database tables to ensure efficiency, accuracy, and no unnecessary

repetition of data.

Continuing immediately with next:

Starting Q12 now! ✅

Thanks for telling clearly.

From now, when I give tables, I will design them properly shaped and aligned (perfect
formatting) like this:
Example:

RollNo Name Subject

1 John Math

1 John Science

This type of neat table (with correct borders and centered) — I will use everywhere now
onward.

✅ I will also continue the next question now with proper tables.
Starting Q12 immediately!

📘 12. Define Functional Dependency and Discuss Its Significance in Schema Refinement. How
Do Functional Dependencies Impact Normalization? 🎯

🧠 What is Functional Dependency?

 Functional Dependency (FD) is a relationship between two attributes, where:

o If you know the value of attribute A, you can determine the value of attribute B.

📘 It is written as:

A→BA \rightarrow B

(Read as "A functionally determines B".)

📘 Real-life Example:

 RollNo → StudentName (If RollNo is known, StudentName is automatically known.)

🔹 Importance of Functional Dependency in Schema Refinement:

 Functional dependencies help in understanding how attributes are related.

 They are used to identify redundancy in a table.

 They guide the normalization process to create better database designs.

📘 Impact of Functional Dependencies on Normalization:

Step Description Example

1 Identify dependencies RollNo → Name, DeptNo

2 Find partial or transitive dependencies DeptNo → DeptName

3 Break large tables into smaller ones Separate Student and Department tables

Create new relations to remove Maintain only necessary attributes in each

4
redundancy table

📘 Example:

Suppose we have this table:

RollNo Name DeptNo DeptName

1 John 10 CS

2 Mary 20 IT

 Functional Dependencies:

o RollNo → Name, DeptNo

o DeptNo → DeptName

👉 DeptName depends on DeptNo, not directly on RollNo (transitive dependency).

Thus, we should split into two tables:

 Student Table (RollNo, Name, DeptNo)

 Department Table (DeptNo, DeptName)

This avoids redundancy and makes database better.

✅ Conclusion:

Functional dependencies are essential tools for designing efficient databases by guiding the
normalization process.
They help to remove repetition, avoid anomalies, and improve database performance.
Ready to continue immediately with Q13 now! ✅
(With properly shaped tables and clean BEFA explanation.)

Continuing immediately with the next 10-mark question:

📘 13. Explain the Concept of Surrogate Keys in the Context of Normalization. Why Are
Surrogate Keys Often Used in Database Design? 🎯

🧠 What is a Surrogate Key?

 A Surrogate Key is a system-generated unique identifier for a record in a table.

 It is artificial (no meaning outside the database).

 It is usually a number (like auto-increment ID).

📘 Real-life example:
Employee ID numbers like 1001, 1002 are surrogate keys. They are not based on employee's
real information like name or birthdate.

🔹 Why Surrogate Keys Are Used?

Reason Explanation

No natural unique
Sometimes, real-world data (like Name, Email) is not unique.
attribute

Simpler and faster Numbers are quicker to search and index than text.

Natural data can change (e.g., Name can change after marriage), but
Stability
surrogate key stays constant.

Easy referencing Other tables can easily refer to surrogate keys as foreign keys.

📘 Example of Surrogate Key:

Suppose we have a Student table:

StudentID (Surrogate Key) Name DOB

1 John 2000-01-01

2 Mary 2001-02-02

 Here, StudentID is the surrogate key.

 Even if John's name changes, StudentID 1 remains the same.

🔹 Surrogate Key vs Natural Key

Surrogate Key Natural Key

System generated Real-world data used

No real-world meaning Has meaning (like Email)

Never changes Can change over time

✅ Conclusion:

Surrogate keys make database design easier and more reliable.

They ensure stability, speed, and simplicity while managing relationships between tables.

Continuing immediately with next:

Starting Q14 now! ✅

Continuing immediately with the next 10-mark question:

📘 14. Discuss the Concept of Multivalued Dependency (MVD). Explain Fourth Normal Form
(4NF) and Provide an Example of a Relation that Violates 4NF and How to Normalize it to 4NF
🎯

🧠 What is Multivalued Dependency (MVD)?

 A Multivalued Dependency (MVD) happens when one attribute depends on another

independently of other attributes.
  In simple words:
One entity can have multiple independent values for two different attributes.

📘 Real-life example:
An employee may have multiple skills and multiple projects independently.

🔹 What is Fourth Normal Form (4NF)?

 A table is in 4NF if:

o It is already in Boyce-Codd Normal Form (BCNF).

o It has no multivalued dependencies unless they are functional dependencies.

📘 Example of a Table Violating 4NF:

Employee Skill Project

John Java Banking

John Python Banking

John Java Insurance

John Python Insurance

📘 Problem:

 Skill and Project are independent for John.

 This results in redundant rows.

🔹 How to Normalize to 4NF?

Split into two separate tables:

Table 1: Employee-Skill

Employee Skill

John Java

John Python
Table 2: Employee-Project

Employee Project

John Banking

John Insurance

 Now, Skill and Project are separated, no redundancy, and each dependency is
independent.

📘 Quick Summary:

Concept Meaning

Multivalued Dependency (MVD) One attribute independently depends on another

4NF Removes multivalued dependency to avoid redundancy

✅ Conclusion:

Fourth Normal Form (4NF) ensures that data is free from multivalued redundancy, making
databases more efficient and clean.

Continuing immediately with next:

Starting Q15 now! ✅

Continuing immediately with the next 10-mark question:

📘 15. What is Fifth Normal Form (5NF)? Explain Its Importance and Give an Example of a
Relation That Violates 5NF. Show How to Decompose It into 5NF 🎯

🧠 What is Fifth Normal Form (5NF)?

 5NF (also called Project-Join Normal Form) deals with complex join dependencies.

 A table is in 5NF if:

o It is already in 4NF.
 o It cannot be broken down into smaller tables without losing data when joined
back.

📘 In simple words:
5NF removes hidden problems caused by complicated relationships between three or more
tables.

🔹 Why Is 5NF Important?

 Avoids unnecessary redundancy in very complex relationships.

 Ensures accurate reconstruction of original data after splitting.

📘 Example of a Table Violating 5NF:

Suppose a table shows Suppliers supplying Parts to Projects:

Supplier Part Project

S1 P1 J1

S1 P2 J1

S2 P1 J2

📘 Problem:
Each supplier supplies multiple parts to multiple projects.
Relationships between Supplier, Part, and Project are mixed and dependent.

🔹 How to Normalize to 5NF?

Split into three separate tables:

Table 1: Supplier-Part

Supplier Part

S1 P1

S1 P2

S2 P1
Table 2: Supplier-Project

Supplier Project

S1 J1

S2 J2

Table 3: Part-Project

Part Project

P1 J1

P2 J1

P1 J2

Now, no redundancy and the original information can be perfectly reconstructed by joining
these tables.

📘 Quick Summary:

Concept Meaning

Fifth Normal Form (5NF) Removes complicated redundancy in join operations

Key Goal Break down complex tables without losing data

✅ Conclusion:

5NF handles complex relationships involving multiple tables and ensures clean, efficient
database structures that support perfect joins.

Continuing immediately with next:

Starting Q16 now! ✅

Continuing immediately with the next 10-mark question:

📘 16. Define Lossless Join and Dependency Preserving Decompositions. Explain How They Are
Used in Normalization and Why They Are Important 🎯

🧠 What is Lossless Join Decomposition?

 Lossless Join Decomposition means:

When a table is split into two or more smaller tables, joining them back gives the
original table exactly without any missing or extra data.

📘 Real-life example:
If you split a Student table into Student details and Course details, and when you join them, you
still get the original full record — it’s a lossless join.

🧠 What is Dependency Preserving Decomposition?

 Dependency Preserving Decomposition means:

After decomposition, all original functional dependencies must still hold true without
needing a complicated join.

📘 Real-life example:
If RollNo → Name remains true even after splitting Student and Address tables, the
decomposition is dependency preserving.

🔹 How Are They Used in Normalization?

During normalization:

 We split large tables to remove redundancy.

 But we must ensure:

o Lossless Join → No data is lost or changed after splitting.

o Dependency Preserving → Rules/relationships between data remain intact

without always doing joins.

Goal: Keep database efficient without data loss and without breaking important relationships.

📘 Example:
Original Table:

RollNo Name DeptNo DeptName

1 John 10 CS

2 Mary 20 IT

Decomposition:

Table 1: Student

RollNo Name DeptNo

1 John 10

2 Mary 20

Table 2: Department

DeptNo DeptName

10 CS

20 IT

 Lossless Join: Joining Student and Department gives back original table.

 Dependency Preserving: RollNo → Name and DeptNo → DeptName are preserved.

📘 Quick Summary:

Concept Meaning

Lossless Join No data lost after splitting

Dependency Preserving Rules still valid without complex joins

Used in Normalization Ensures clean, accurate database designs

✅ Conclusion:

Lossless join and dependency preserving decompositions are essential in normalization to

maintain data integrity, consistency, and efficiency in relational databases.
✅✅✅
Now all Unit 4 – 2 Marks and 10 Marks questions COMPLETED FULLY with clean explanations!

If you want, I am ready to immediately start Unit 5 – 2 Marks Questions in the same BEFA
simple style!
Say Start Unit 5 ✅ if you want to continue!