# Is 3NF decomposition dependency preserving?

## Is 3NF decomposition dependency preserving?

Now if we decompose it and make the decomposition 3NF, then it is possible to satisfy both lossless and dependency preserving. i.e., for any relation there always exist a decomposition to 3NF, which is guaranteed to satisfy both the given properties.

## How do you decompose into 3rd normal form?

How to decompose this relation into 3NF relations?

1. Find a minimal basis of F, say G.
2. For each FD X → A in G, use {X, A} as the schema of one of the relations in the decomposition.
3. If none of the sets of relations from Step2 is a superkey for R, add another relation whose schema is a key for R.

Which decomposition is dependency preserving?

The relational R is decomposed into R1(ABC) and R2(AD) which is dependency preserving because FD A->BC is a part of relation R1(ABC).

Does the decomposition preserve dependencies?

The dependencies are preserved because each dependency in F represents a constraint on the database. If decomposition is not dependency-preserving, some dependency is lost in the decomposition.

### Is 3NF decomposition always lossless?

The statement: 3NF ensures lossless decomposition while BCNF does not.

### Which normalization ensures lossless decomposition?

Now, we can check the first condition for Lossless-join decomposition. The union of sub relation R1 and R2 is the same as relation R. The relation is the same as the original relation R. Hence, the above decomposition is Lossless-join decomposition….R2 (B, C)

B C
36 09
42 30

What is transitive dependency in 3NF?

A relation that is in First and Second Normal Form and in which no non-primary-key attribute is transitively dependent on the primary key, then it is in Third Normal Form (3NF). Note – If A->B and B->C are two FDs then A->C is called transitive dependency.

Is BCNF dependency preserving?

BCNF can be used to obtain a lossless join decomp into 3NF (typically, can stop earlier) but does not ensure dependency preservation.

#### What is lossless decomposition and dependency preservation?

Relation R is decomposed into two or more relations if decomposition is lossless join as well as dependency preserving. Lossless Join Decomposition. If we decompose a relation R into relations R1 and R2, Decomposition is lossy if R1 ⋈ R2 ⊃ R. Decomposition is lossless if R1 ⋈ R2 = R.

#### What are the advantages of 3NF?

The Third Normal Form removes the redundancy effectively so the data becomes consistent as well as maintains the data integrity. As the redundancy is reduced, the database becomes less in size and also the duplication of data is reduced which also improves the performance.

How do you check whether a relation is dependency preserving or not?

Now check F ⊂ F1 ⋃ F2, this means we check all FDs of F are present in the set of FDs (F1 ∪ F2) or not. If present then it is dependency preserving otherwise not. F1 ∪ F2 = {A → B, B → C} and also derive A → C from the transitive property.

Is 4nf decomposition dependency preserving?

This decomposition is not dependency preserving as it fails to preserve .

## What does dependency preserving mean?

In order for a decomposition to be dependency preserving, the database system must be able to check each functional dependency of the original F locally in one of the decomposed relations, without having to perform any joins.

## What is the third rule to normalize a database?

Third normal form Eliminate fields that do not depend on the key.