How do you find the decomposition of a 3NF?

How do you find the decomposition of a 3NF?

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.

How do you find a 3NF relationship?

A relation is in third normal form, if there is no transitive dependency for non-prime attributes as well as it is in second normal form. A relation is in 3NF if at least one of the following condition holds in every non-trivial function dependency X –> Y: X is a super key.

How do you know if decomposition is lossless?

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.

What is good decomposition in DBMS?

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.

How do you BCNF decomposition?

Steps:

1. Identify the dependencies which violates the BCNF definition and consider that as X->A.
2. Decompose the relation R into XA & R-{A} (R minus A).
3. Validate if both the decomposition are in BCNF or not. If not re-apply the algorithm on the decomposition that is not in BCNF.

Does 3NF guarantee lossless join?

The statement: 3NF ensures lossless decomposition while BCNF does not. (R1,R2) is a lossless-join decomposition of R with respect to a set of FDs F if for every instance r of R that satisfies F: πR1(r) ⋈ πR2(r) = r.

Is there a way to check if BCNF is in 3NF?

The steps are the same with checking for BCNF. Our only FD’s left hand side is equal to that candidate key, so it is in 3NF. Honestly, you don’t need to check for 3NF for the first example, because all relation that is in BCNF is also in 3NF.

When to use third normal form ( 3NF )?

X is a super key. Y is a prime attribute (each element of Y is part of some candidate key). 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.

How to decompose BCNF into an example?

Decomposition into BCNF Example 1 Let’s take R=ABCDE, F = {A -> BC, C -> DE) First, let’s compute the attribute closure: A+ = ABCDE B+ = B C+ = CDE D+ = D E+ = E Inspecting this attribute closure tells us the candidate keys for R are A. Now that we know the candidate keys, we can begin to decompose it. Looking at the 1stFD in F, A -> BC.

When is a relation in a 3NF form?

A relation is in 3NF if at least one of the following condition holds in every non-trivial function dependency X –> Y: X is a super key. Y is a prime attribute (each element of Y is part of some candidate key).