Contents
- 1 What do you mean by lossless join and dependency preserving relations?
- 2 What is lossless join dependency?
- 3 Is Bcnf is lossless join and dependency preserving?
- 4 What do you mean by dependency preservation?
- 5 Why is 3NF dependency preserving?
- 6 What do you mean by dependency preserving?
- 7 Which is the correct decomposition for dependency preserving decomposition?
- 8 When is decomposition done in a relational model?
What do you mean by lossless join and dependency preserving relations?
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 is lossless join dependency?
In database design, a lossless join decomposition is a decomposition of a relation into relations. such that a natural join of the two smaller relations yields back the original relation. This is central in removing redundancy safely from databases while preserving the original data.
Is Bcnf is lossless join and 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 the lossless join property of decomposition?
Lossless join decomposition is a decomposition of a relation R into relations R1,R2 such that if we perform natural join of two smaller relations it will return the original relation. This is effective in removing redundancy from databases while preserving the original data..
Why is dependency preserving important?
Dependency Preserving It is an important constraint of the database. In the dependency preservation, at least one decomposed table must satisfy every dependency.
What do you mean by dependency preservation?
The dependency preservation decomposition is another property of decomposed relational database schema D in which each functional dependency X -> Y specified in F either appeared directly in one of the relation schemas Ri in the decomposed D or could be inferred from the dependencies that appear in some Ri.
Why is 3NF dependency preserving?
It is always possible to find a dependency-preserving lossless-join decomposition that is in 3NF. A database design is in 3NF if each member of the set of relation schemas is in 3NF. We now allow functional dependencies satisfying only the third condition.
What do you mean by dependency preserving?
Can a relation be both lossless join and dependency preserving?
A relation R is decomposed into two or more only if the decomposition is both lossless join and dependency preserving. Learn more about Other Decompositions here on this page.
Why is FD a-> BC Lossless Join Decomposition?
This is lossless join decomposition because Suppose a relation R (A,B,C,D) with FD set {A->BC} is decomposed into R1 (ABC) and R2 (AD) which is dependency preserving because FD A->BC is a part of R1 (ABC)
Which is the correct decomposition for dependency preserving decomposition?
Hence the decomposition is not lossless. For dependency preserving decomposition, A->B can be ensured in R1 (AB) and C->D can be ensured in R2 (CD). Hence it is dependency preserving decomposition. So, the correct option is C. This article is contributed by Sonal Tuteja.
When is decomposition done in a relational model?
Decomposition of a relation is done when a relation in relational model is not in appropriate normal form. Relation R is decomposed into two or more relations if decomposition is lossless join as well as dependency preserving.