Dependency Preservation ensures that no functional dependencies are lost during the decomposition process.

Dependency Preservation is a crucial concept in database normalization, particularly when decomposing relations into smaller, more manageable pieces. Here's a concise explanation:

Understanding Dependency Preservation

1. Definition: Dependency Preservation means that if a relation is decomposed into multiple relations, all the functional dependencies that held in the original relation should still hold in the decomposed relations.

2. Importance: This property is vital to ensure that the integrity of the database is maintained after decomposition. Losing functional dependencies can lead to anomalies and inconsistent data.

3. Decomposition Process: When decomposing a relation, we aim to minimize redundancy and avoid data anomalies. However, we must ensure that all original functional dependencies can be derived from the set of functional dependencies in the new relations.

4. Example Scenario:

   • Suppose we have a relation R(A, B, C) with functional dependencies F: {A → B, B → C}.
   • If we decompose R into R1(A, B) and R2(B, C), we need to check if the original functional dependencies can be derived from R1 and R2.
   • This means ensuring that there exists a way to infer A → B and B → C from R1 and R2.

5. Testing for Dependency Preservation: Utilize techniques like the closure of attributes or functional dependency preservation checks to validate that no dependencies are lost after decomposition.

In summary, dependency preservation ensures the functional relationships are maintained during database design and restructuring, safeguarding data integrity and adherence to business rules.