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Decomposition in DBMS: Importance, Types, and Advanced Techniques

Q: What are the advanced decomposition techniques in DBMS?

Advanced techniques include: Boyce-Codd Normal Form (BCNF): Ensures every determinant is a candidate key. Fourth Normal Form (4NF): Eliminates multi-valued dependencies. Third Normal Form (3NF): Reduces transitive dependencies. Second Normal Form (2NF): Eliminates partial dependencies.

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Are you struggling with messy, inconsistent data in your database? Do duplicate entries and anomalies slow down your system?

Decomposition in DBMS is your solution.

In DBMS, decomposition can be defined as an approach of subdividing a large table into even smaller ones so as to solve complex and large problems. This practice works towards the improvement of quality, reduction of time and effort, as well as eradication of multiple entries of similar data.

In this blog, we will look at what decomposition in DBMS is, why it matters, different types, properties, and more advanced concepts in decomposition and look at the strengths and weaknesses as well.

Decomposition in DBMS

Importance of Decomposition in DBMS

To effectively manage the cleanliness of the database, decomposition plays an important role. The large tables can be divided into smaller ones, which will allow you to avoid any discrepancies in the data.

Here’s why decomposition matters:

Improves Data Integrity: Ensures that all data remains accurate and consistent.
Optimises Storage: Reduces redundancy and saves storage space.
Enhances Performance: Makes database operations faster and more efficient.

Imagine managing a library. You don’t have one enormous list of all books but rather have subdivisions based on the genre: fiction, non-fiction, etc. This makes it easy for youths to locate and organise books. This makes it easier to find and manage books. Similarly, decomposition organises data in a database.

Different Types of Decomposition in DBMS

Understanding the types of decomposition is key to applying the right one for your needs. We can categorise decomposition into two types:

Lossless Decomposition
Lossy Decomposition

Let’s understand them one by one.

Decomposition in DBMS

Lossless Decomposition: Ensuring No Data Loss

Lossless decomposition means splitting a table without losing any data. When we join the decomposed tables, we get back to the original table.

This is like cutting a cake into slices and then putting it back together perfectly.

Example

Consider a table StudentCourse:

StudentID	StudentName	CourseID	CourseName
1	Divya	101	Math
2	Rahul	102	Science

We decompose it into:

1. Student Table:

StudentID	StudentName	CourseID
1	Divya	101
2	Rahul	102

2. Course Table:

CourseID	CourseName
101	Math
102	Science

By joining these on CourseID, we get the original StudentCourse table back.

Here’s how to do it in Python:

# Example to demonstrate lossless decomposition

# Input data

students = [

{"StudentID": 1, "StudentName": "Divya", "CourseID": 101},

{"StudentID": 2, "StudentName": "Rahul", "CourseID": 102}

]

courses = [

{"CourseID": 101, "CourseName": "Math"},

{"CourseID": 102, "CourseName": "Science"}

]

# Display original data

print("Original Student Data:")

for student in students:

print(student)

print("nOriginal Course Data:")

for course in courses:

print(course)

# Join operation

result = []

for student in students:

for course in courses:

if student["CourseID"] == course["CourseID"]:

result.append({**student, "CourseName": course["CourseName"]})

# Display joined data

print("nJoined Data (Lossless):")

for row in result:

print(row)

Output:

Original Student Data:

{'StudentID': 1, 'StudentName': 'Divya', 'CourseID': 101}

{'StudentID': 2, 'StudentName': 'Rahul', 'CourseID': 102}

 

Original Course Data:

{'CourseID': 101, 'CourseName': 'Math'}

{'CourseID': 102, 'CourseName': 'Science'}

 

Joined Data (Lossless):

{'StudentID': 1, 'StudentName': 'Divya', 'CourseID': 101, 'CourseName': 'Math'}

{'StudentID': 2, 'StudentName': 'Rahul', 'CourseID': 102, 'CourseName': 'Science'}

Lossy Decomposition: Potential for Data Loss

Lossy decomposition might result in losing some data when we split and then rejoin tables. This is like cutting a cake and losing some crumbs.

Example

Consider a table EmployeeProject:

EmpID	EmpName	ProjectID	Hours
1	Amit	201	20
2	Anamika	202	30

We decompose it into:

1. Employee Table:

EmpID	EmpName
1	Amit
2	Anamika

2. Project Table:

ProjectID	Hours
201	20
202	30

Rejoining these might not accurately recreate the original EmployeeProject table.

Here’s how a lossy decomposition might look in Python:

# Example to demonstrate lossy decomposition

# Input data

employees = [

{"EmpID": 1, "EmpName": "Amit"},

{"EmpID": 2, "EmpName": "Anamika"}

]

projects = [

{"ProjectID": 201, "Hours": 20},

{"ProjectID": 202, "Hours": 30}

]

# Display original data

print("Original Employee Data:")

for employee in employees:

print(employee)

print("nOriginal Project Data:")

for project in projects:

print(project)

# Join operation (illustrative, showing the potential loss)

result = []

for employee in employees:

for project in projects:

result.append({**employee, **project})

# Display joined data

print("nJoined Data (Lossy):")

for row in result:

print(row)

Output:

Original Employee Data:

{'EmpID': 1, 'EmpName': 'Amit'}

{'EmpID': 2, 'EmpName': 'Anamika'}

 

Original Project Data:

{'ProjectID': 201, 'Hours': 20}

{'ProjectID': 202, 'Hours': 30}

 

Joined Data (Lossy):

{'EmpID': 1, 'EmpName': 'Amit', 'ProjectID': 201, 'Hours': 20}

{'EmpID': 1, 'EmpName': 'Amit', 'ProjectID': 202, 'Hours': 30}

{'EmpID': 2, 'EmpName': 'Anamika', 'ProjectID': 201, 'Hours': 20}

{'EmpID': 2, 'EmpName': 'Anamika', 'ProjectID': 202, 'Hours': 30}

Here, the original relationships between employees and projects are lost, leading to incorrect data.

Key Properties of Decomposition in DBMS

When decomposing tables, keeping these properties in mind ensures success.

Ensuring a Lossless Join in Decomposition

A lossless join is critical. It means that when we join decomposed tables, we should get back to the original table exactly as it was. Here’s how we can ensure a lossless join:

Union of Attributes: The combined attributes of the decomposed tables must cover all attributes of the original table.
Common Attribute: There should be at least one common attribute between the decomposed tables, which acts as a superkey.

Maintaining Dependency Preservation During Decomposition

Dependency preservation ensures that all functional dependencies are maintained in the decomposed tables. This is important for maintaining the logical relationships between data.

Reducing Data Redundancy Through Decomposition

Reducing redundancy means eliminating duplicate data entries. This makes the database more efficient and easier to manage.

Enhancing Database Efficiency

By decomposing tables, we can improve database performance. Smaller, well-structured tables make queries and updates faster and more efficient.

Maintaining Data Integrity and Consistency

Decomposition ensures that data remains accurate and consistent. By breaking down tables, we can manage data anomalies better and ensure consistency across the database.

Exploring Lossless Decomposition with Unique Examples

Lossless decomposition ensures that no data is lost when splitting a table. It’s like cutting a cake and being able to piece it back together perfectly. But how do we ensure this?

Criteria for a Lossless Join Decomposition

For a decomposition to be lossless, it must meet these criteria:

Cover All Attributes: The decomposed tables must include all attributes of the original table.
Common Superkey: There must be a common attribute that acts as a superkey in one or both tables.

These criteria ensure that we can perfectly recreate the original table by joining the decomposed tables.

Practical Example of a Lossless Decomposition

Imagine a table StudentCourse with columns: StudentID, StudentName, CourseID, and CourseName. Here’s what the table looks like:

StudentID	StudentName	CourseID	CourseName
1	Neha	101	Math
2	Rohan	102	Science

We can decompose it into two tables:

1. Student Table:

StudentID	StudentName	CourseID
1	Neha	101
2	Rohan	102

2. Course Table:

CourseID	CourseName
101	Math
102	Science

When we join these tables on CourseID, we can reconstruct the original StudentCourse table perfectly.

Here’s how you can do it with Python:

    
# Example to demonstrate lossless decomposition 

# Input data

students = [

{"StudentID": 1, "StudentName": "Neha", "CourseID": 101},

{"StudentID": 2, "StudentName": "Rohan", "CourseID": 102}

] 

courses = [

{"CourseID": 101, "CourseName": "Math"},

{"CourseID": 102, "CourseName": "Science"}

] 

# Display original data

print("Original Student Data:")

for student in students:

print(student) 

print("nOriginal Course Data:")

for course in courses:

print(course)
 

# Join operation

result = []

for student in students:

for course in courses:

if student["CourseID"] == course["CourseID"]:

result.append({**student, "CourseName": course["CourseName"]})
 

# Display joined data

print("nJoined Data (Lossless):")

for row in result:
print(row)

Output:

Original Student Data: 
{'StudentID': 1, 'StudentName': 'Neha', 'CourseID': 101} 
{'StudentID': 2, 'StudentName': 'Rohan', 'CourseID': 102}   
Original Course Data: 
{'CourseID': 101, 'CourseName': 'Math'} 
{'CourseID': 102, 'CourseName': 'Science'}   
Joined Data (Lossless): 
{'StudentID': 1, 'StudentName': 'Neha', 'CourseID': 101, 'CourseName': 'Math'} 
{'StudentID': 2, 'StudentName': 'Rohan', 'CourseID': 102, 'CourseName': 'Science'}

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Understanding Lossy Decomposition with Practical Scenarios

Lossy decomposition can lead to data loss. In database terms, this means losing some information when tables are split and rejoined.

Identifying Characteristics of Lossy Decomposition

Signs of lossy decomposition include:

Extra or Missing Tuples: The joined table has more or fewer rows than the original.
Data Inconsistency: Relationships between data are not preserved.

Practical Example of a Lossy Decomposition

Consider a table EmployeeProject:

EmpID	EmpName	ProjectID	Hours
1	Navin	201	20
2	Nancy	202	30

If we decompose it into:

1. Employee Table:

EmpID	EmpName
1	Navin
2	Nancy

2. Project Table:

ProjectID	Hours
201	20
202	30

We lose the direct relationship between employees and their projects. Here’s a Python example:

# Example to demonstrate lossy decomposition 

# Input data

employees = [

{"EmpID": 1, "EmpName": "Navin"},

{"EmpID": 2, "EmpName": "Nancy"}

] 

projects = [

{"ProjectID": 201, "Hours": 20},

{"ProjectID": 202, "Hours": 30}

] 

# Display original data

print("Original Employee Data:")

for employee in employees:

print(employee)

print("nOriginal Project Data:")

for project in projects:

print(project) 

# Join operation (illustrative, showing the potential loss)

result = []

for employee in employees:

for project in projects:

result.append({**employee, **project}) 

# Display joined data

print("nJoined Data (Lossy):")

for row in result:

print(row)

Output:

Original Employee Data:

{'EmpID': 1, 'EmpName': 'Navin'}

{'EmpID': 2, 'EmpName': 'Nancy'} 

Original Project Data:

{'ProjectID': 201, 'Hours': 20}

{'ProjectID': 202, 'Hours': 30} 

Joined Data (Lossy):

{'EmpID': 1, 'EmpName': 'Navin', 'ProjectID': 201, 'Hours': 20}

{'EmpID': 1, 'EmpName': 'Navin', 'ProjectID': 202, 'Hours': 30}

{'EmpID': 2, 'EmpName': 'Nancy', 'ProjectID': 201, 'Hours': 20}
{'EmpID': 2, 'EmpName': 'Nancy', 'ProjectID': 202, 'Hours': 30}

Advanced Decomposition Techniques in DBMS

To keep your data clean and efficient, we can use advanced techniques like BCNF, 4NF, 3NF, and 2NF. These methods help ensure our data is well-organised and free from anomalies.

Boyce-Codd Normal Form (BCNF) in Decomposition

BCNF addresses redundancy and dependency issues more rigorously than 3NF. In BCNF, every determinant must be a candidate key. This means any attribute that determines another attribute must uniquely identify a row.

Example of BCNF

Consider a table InstructorCourse:

InstructorID	CourseID	Room
1	101	A101
1	102	B202
2	101	A101

To decompose it to BCNF:

1. Instructor Table:

InstructorID	CourseID
1	101
1	102
2	101

2. Room Table:

CourseID	Room
101	A101
102	B202

Fourth Normal Form (4NF) for Eliminating Multi-Valued Dependencies

4NF deals with multi-valued dependencies. A table in 4NF has no multi-valued dependencies, ensuring cleaner data.

Example of 4NF

Consider a table EmployeeSkills:

EmpID	Skill	ProjectID
1	Python	301
1	SQL	302
2	Python	301

To decompose it to 4NF:

1. EmployeeSkills Table:

EmpID	Skill
1	Python
1	SQL
2	Python

2. EmployeeProjects Table:

EmpID	ProjectID
1	301
1	302
2	301

Third Normal Form (3NF) for Reducing Transitive Dependencies

3NF ensures that non-key attributes depend only on the primary key. This reduces transitive dependencies, making the data more straightforward.

Example of 3NF

Consider a table EmployeeDetails:

EmpID	EmpName	DeptID	DeptName
1	Preksha	101	HR
2	Murali	102	Finance

To decompose it to 3NF:

1. Employee Table:

EmpID	EmpName	DeptID
1	Preksha	101
2	Murali	102

2. Department Table:

DeptID	DeptName
101	HR
102	Finance

Second Normal Form (2NF) for Eliminating Partial Dependencies

2NF eliminates partial dependencies. Every non-key attribute must be fully dependent on the primary key, not just part of it.

Example of 2NF

Consider a table CourseEnrollment:

StudentID	CourseID	Grade
1	101	A
2	102	B

To decompose it to 2NF:

1. Enrollment Table:

StudentID	CourseID
1	101
2	102

2. Grades Table:

CourseID	Grade
101	A
102	B

Benefits of Implementing Decomposition in DBMS

Reduction of Data Redundancy

Decomposition breaks down large tables into smaller ones, removing duplicate data entries. This saves storage space and makes data management easier.

Improved Data Integrity

Smaller, focused tables help maintain data accuracy. When each table serves a specific purpose, errors become easier to spot and correct.

Enhanced Query Performance

Decomposition speeds up database queries. When data is organised into smaller, logical tables, the database can find information faster.

Simplified Data Maintenance

Updating data becomes simpler with decomposition. Changes need to be made in only one place, reducing the risk of errors.

Flexibility in Database Design

Decomposition allows for a more flexible database design. You can add or remove tables without disrupting the entire database.

Challenges and Disadvantages of Decomposition in DBMS

Complexity in Querying

Decomposed tables can make querying more complex. You might need to join multiple tables to get the information you need.

Potential Data Loss

Improper decomposition can lead to data loss. It’s crucial to ensure that all necessary relationships are preserved.

Increased Storage Overhead

More tables mean more storage. Even though decomposition reduces redundancy, it can increase the overall number of tables, which requires more storage space.

Dependency Maintenance

Maintaining dependencies between tables can be tricky. If not managed well, it can lead to data inconsistencies.

Conclusion

We looked at the vital function of decomposition in DBMS in this blog.

We’ve seen how dividing huge tables into smaller, more manageable ones may assist in improving data integrity, decreasing data redundancy, and increasing query performance.

We examined both lossless and lossy decomposition, understanding their importance and potential pitfalls.

Advanced decomposition techniques, such as BCNF, 4NF, 3NF, and 2NF, ensure our databases remain efficient and free from anomalies.

By carefully implementing decomposition, we can maintain a clean, efficient, and flexible database system. The key is to balance the benefits while addressing the challenges to achieve optimal database management.

FAQs

What is the difference between lossless and lossy decomposition?

Lossless decomposition ensures no data is lost when splitting and rejoining tables. Lossy decomposition may result in data loss or extra, unnecessary data.

Why is dependency preservation important in decomposition?

Dependency preservation maintains the logical relationships between data. It ensures that the decomposed tables still reflect the original table’s functional dependencies.

How does decomposition reduce data redundancy?

Decomposition splits a table into smaller tables. This process removes duplicate data entries, making the database more efficient.

What are the key criteria for a lossless join decomposition?

For a lossless join decomposition:

The decomposed tables must cover all attributes of the original table.
There must be a common attribute acting as a superkey in one or both tables.

What are the advanced decomposition techniques in DBMS?

Advanced techniques include:

Boyce-Codd Normal Form (BCNF): Ensures every determinant is a candidate key.
Fourth Normal Form (4NF): Eliminates multi-valued dependencies.
Third Normal Form (3NF): Reduces transitive dependencies.
Second Normal Form (2NF): Eliminates partial dependencies.

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