Contents
- 1 How can we preserve functional dependencies during decomposition?
- 2 Are dependencies preserved by the decomposition?
- 3 Is 3NF dependency preserving and lossless?
- 4 How is functional dependency preserved when normalization to BCNF?
- 5 How is the BCNF decomposition algorithm used in data science?
- 6 Which is the dependency which violates the BCNF definition?
How can we preserve functional dependencies during decomposition?
Dependency Preserving In the dependency preservation, at least one decomposed table must satisfy every dependency. If a relation R is decomposed into relation R1 and R2, then the dependencies of R either must be a part of R1 or R2 or must be derivable from the combination of functional dependencies of R1 and R2.
Are dependencies preserved by the decomposition?
The dependencies are preserved because each dependency in F represents a constraint on the database. If decomposition is not dependency-preserving, some dependency is lost in the decomposition.
Why is Bcnf not dependency preserving?
To convert this relation into bcnf decompose into two relations : R1(a b ) {a->b} key = a R2(a c d e) {ac->de} key =a Both R1 and R2 are in bcnf as every determinant is a key, but they are not dependency preserving as bd->e is lost.
Is 3NF dependency preserving and lossless?
i.e., for any relation there always exist a decomposition to 3NF, which is guaranteed to satisfy both the given properties. For BCNF, the decomposition is not guaranteed to satisfy both the properties. Sometimes when lossless property is satisfied, dependency preserving is no longer possible.
How is functional dependency preserved when normalization to BCNF?
Note also that in this case, functional dependency is preserved but normalization to BCNF does not guarantee this. According to given FD set “ACE” forms the key. Clearly R (A,B,C,D,E) is not in 2NF. 2NF decomposition gives R1 (A,B) , R2 (C,D) and R3 (A,C,E). this decomposition decomposed relations are in 3NF and also in BCNF.
Can a decomposition that is not in BCNF be lossless?
If not re-apply the algorithm on the decomposition that is not in BCNF. All the decomposition resulted by this algorithm would be in BCNF and they would be lossless however some of the decomposition will preserved the dependencies and rest not. BCNF is not a preferred normal form as it does not guarantee for dependency preservation.
How is the BCNF decomposition algorithm used in data science?
BCNF Decomposition | A step by step approach. BCNF algorithm: It is used to decompose any given relation to BCNF directly. This algorithm gives guarantee for: Final BCNF decomposition.
Which is the dependency which violates the BCNF definition?
Hence Prime Attributes: A, B. Non Prime Attributes: C, D, E. Hence the dependency which violates BCNF are D -> E, A -> C, B -> D. so will take one by one the dependencies which violates the BCNF definition. so will take D -> E first as X -> ‘A’ {not the A listed in relation as attributes} So X = D & ‘A’ = E.