Lossless Decomposition in DBMS

DBMS | Lossless Decomposition: In this tutorial, we will learn about Lossless Decomposition, the conditions to achieve Lossless Decomposition, and its advantages and disadvantages. By Pratishtha Saxena Last updated : May 31, 2023

When a relation is decomposed into multiple smaller relations, lossless decomposition ensures that the original information contained in the original relation can be reconstructed by joining the decomposed relations using suitable join operations.

What is Lossless Decomposition in DBMS?

Lossless decomposition, also known as lossless join property or lossless-join decomposition, is a desirable property in database normalization and decomposition within database management systems (DBMS).

It refers to the ability to recreate the original relation or relations through the process of joining the decomposed relations, without losing any information or introducing spurious tuples.

How to Achieve Lossless Decomposition in DBMS?

To achieve lossless decomposition, two main conditions must be satisfied:

  1. Dependency Preservation: The decomposed relations should preserve all the functional dependencies that existed in the original relation.
  2. Common Attribute: There should be at least one common attribute shared by the decomposed relations. This attribute enables the join operation to recreate the original relation without any loss of information.

Lossless decomposition is important because it ensures that the decomposition process does not introduce any information loss or anomalies in the resulting relations. It helps maintain the integrity and correctness of the database.

Lossless decomposition is a key consideration in database normalization techniques such as Boyce-Codd Normal Form (BCNF) and Third Normal Form (3NF). These normal forms aim to decompose relations into smaller, well-structured relations while preserving dependencies and avoiding anomalies.

Advantages of Lossless Decomposition

  1. Data Integrity: Lossless decomposition ensures that the original information in the database is preserved without any loss or corruption.
  2. Dependency Preservation: Lossless decomposition preserves all the functional dependencies that exist in the original relation.
  3. Database Normalization: Lossless decomposition is a key component of the normalization process. It helps eliminate redundancy, minimize data anomalies, and improve overall database structure and design.
  4. Efficient Join Operations: Lossless decomposition allows for efficient join operations between decomposed relations.

Disadvantages of Lossless Decomposition

  1. Increased Storage Requirements: Lossless decomposition can result in an increased number of relations or tables compared to the original relation.
  2. Complex Querying: Decomposing a relation into smaller relations can make complex querying more challenging.
  3. Performance Impact: The decomposition process and subsequent join operations can impact performance, especially when dealing with large databases or complex queries.
  4. Maintenance Complexity: Managing and maintaining a decomposed database with multiple relations can be more complex than managing a single relation.

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