Does BCNF decomposition guarantee lossless join?
BCNF can be used to obtain a lossless join decomp into 3NF (typically, can stop earlier) but does not ensure dependency preservation.
Which decomposition gives a lossless join?
Lossless join decomposition is a decomposition of a relation R into relations R1, R2 such that if we perform a natural join of relation R1 and R2, it will return the original relation R. This is effective in removing redundancy from databases while preserving the original data…
Why there is no lossless join dependency preserving decomposition into BCNF?
The only candidate key of the original relation is {BD} . So, the decomposition in 3NF that you propose is not lossless, since no relation schema contains both attributes. This decomposition preserves both data and dependencies. Moreover, all the schemas satisfy also the BCNF.
Is there a lossless join and dependency preserving BCNF decomposition of R?
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.
Is 3NF always lossless join?
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.
Which normalization ensures lossless decomposition?
Now, let us check whether this decomposition is lossless or not. This relation is same as the original relation R….Example-
| A | B | C |
|---|---|---|
| 2 | 5 | 3 |
| 3 | 3 | 3 |
Is R in BCNF?
Is R in BCNF? No – because in the FD A->B, A is not a superkey (it is only part of a key).
How lossless decomposition is useful?
Decomposition is lossless if it is feasible to reconstruct relation R from decomposed tables using Joins. This is the preferred choice. The information will not lose from the relation when decomposed. The join would result in the same original relation.
What is meant by lossless join decomposition?
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.
What is lossless decomposition in database how it is useful in database 7?
What is lossless join property in DBMS?
The lossless join property is a feature of decomposition supported by normalisation. It is the ability to ensure that any instance of the original relation can be identified from corresponding instances in the smaller relations.
Are all BCNF lossless?
1 Answer. The statement: 3NF ensures lossless decomposition while BCNF does not.
What is an example of Lossless Join Decomposition?
For Example, A relation R (A, B, C, D) with FD set {A->BC} is decomposed into R1 (ABC) and R2 (AD) which is a lossless join decomposition as: First condition holds true as Att (R1) U Att (R2) = (ABC) U (AD) = (ABCD) = Att (R). Second condition holds true as Att (R1) ∩ Att (R2) = (ABC) ∩ (AD) ≠ Φ
How to check for lossless join decomposition using fd set?
To check for lossless join decomposition using FD set, following conditions must hold: Union of Attributes of R1 and R2 must be equal to attribute of R. Each attribute of R must be either in R1 or in R2.
What is the difference between lossy and lossless decompositions?
The decompositions R1, R2, R2…Rn for a relation schema R are said to be Lossless if there natural join results the original relation R. The decompositions R1, R2, R2…Rn for a relation schema R are said to be Lossy if there natural join results into addition of extraneous tuples with the original relation R.
Is attatt(R1) = att(R2) Lossless Join Decomposition?
Att (R1) ∩ Att (R2) = Φ, which violates the condition of lossless join decomposition. Hence the decomposition is not lossless. A->B can be ensured in R1 (AB) and C->D can be ensured in R2 (CD).