How does BCNF decompose?

Example in Decomposition into BCNF

Table of Contents

Relation: A B C D E F G H I J K L M Functional dependencies: A -> B C D E E -> F G H I -> J A I -> K A L -> M.
First: Find all keys.
Check R for BCNF condition:
Decompose:
Check R1 for BCNF condition:
Decompose:
Check R11 for BCNF condition:
Check R12 for BCNF condition:

Does BCNF ensure lossless decomposition?

3NF ensures lossless decomposition while BCNF does not.

Is BCNF decomposition always possible?

It is known that it is not always possible to obtain a lossless functional dependency (FD)-preserving BCNF decomposition. (This decomposition is called a perfect BCNF decomposition for short.) Example 1 Let U be a universal relation scheme and F be a set of functional dependencies over U.

Is BCNF decomposition unique?

No it’s not unique.

What is the condition of BCNF?

A table is in BCNF if every functional dependency X->Y, X is the super key of the table. For BCNF, the table should be in 3NF, and for every FD. LHS is super key.

Why is BCNF decomposition lossless?

The decomposition of R into X and Y is lossless with respect to F if and only if the closure of F contains: X ∩ Y → X, or X ∩ Y → Y in example: decomposing ABC into AB and BC is lossy, because intersection (i.e., “B”) is not a key of either resulting relation.

Why is BCNF stronger than 3NF?

BCNF is a stronger form of normalization than 3NF because it eliminates the second condition for 3NF, which allowed the right side of the FD to be a prime attribute. Thus, every left side of an FD in a table must be a superkey.

What is the advantage of BCNF?

It is a more restricted form of normalization so that the database does not end in anomalies. The business rules expressed in functional dependencies are enforced using keys, and BCNF ensures that it is correctly followed.

Which is stronger BCNF or 3NF?

How can I satisfy my BCNF?

Rules for BCNF For a table to satisfy the Boyce-Codd Normal Form, it should satisfy the following two conditions: It should be in the Third Normal Form. And, for any dependency A → B, A should be a super key.

What is difference between 3NF and BCNF?

BCNF is an extension of 3NF and it is has more strict rules than 3NF. Also, it is considered to be more stronger than 3NF. This relation is in BCNF as it is already in 3Nf (there is no prime attribute deriving no prime attribute) and on the left hand side of the functional dependency there is a candidate key.

Is BCNF lossless 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.

Is BCNF better than 2nf and 3NF Why?

This relation is in 3NF as it is already in 2NF and has no transitive dependency. Also there is no non prime attribute that is deriving a non prime attribute….Difference between 3NF and BCNF :

S.NO.	3NF	BCNF
2.	It is less stronger than BCNF.	It is comparatively more stronger than 3NF.

How do you know if a decomposition is lossless join?

Decomposition is lossy if R1 ⋈ R2 ⊃ R. Decomposition is lossless if R1 ⋈ R2 = R….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.
Intersection of Attributes of R1 and R2 must not be NULL.

Does BCNF Guaranty lossless decomposition does BCNF Guaranty dependency preservation?

For BCNF, the decomposition is not guaranteed to satisfy both the properties. Sometimes when lossless property is satisfied, dependency preserving is no longer possible.

Does BCNF decomposition procedure always preserve all functional dependencies?

Well, the answer is simply that such algorithm, even if applied by eliminating the FD that violates the BCNF in any order, does not guarantee to find all the possibile decompositions (and does not guarantee either that the solutions found preserve the dependencies).