Which decomposition gives a lossless join?

Which decomposition gives a lossless join?

Relation R is decomposed into two or more relations if decomposition is lossless join as well as dependency preserving. 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.

How do you know if a decomposition is in BCNF?

In fact, to check that a relation is BCNF, we can check if all the dependecies of a cover have the determinant which is a superkey. In your case this is true (since the candidate keys of the relation are A , B , and E ), so there is no need to decompose it.

How to do Lossless Join Decomposition in DBMS?

What is lossless join decomposition in DBMS? 1 R (A, B, C) 2 R1 (A, B) 3 R2 (B, C) 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. 4 R1U R2 = R. The relation is the same as the original relation R. Hence, the above decomposition is Lossless-join decomposition.

What’s the difference between a lossy decomposition and a lossless decomposition?

The decompositions R1, R2, R2…Rn for a relation schema R are said to be Lossy if there natural join results into additon of extraneous tuples with the the original relation R. Formally, Let R be a relation and R1, R2, R3 … Rn be it’s decomposition, the decomposition is lossless if – Formally, Let R be a relation and R1, R2, R3 …

How to check 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.

Is the decomposition of ATT ( R1 ) lossless?

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).