CODEWITHSUNDEEP
databaserdbmsdatabase-normalizationfunctional-dependenciesbcnf
asdf
asdf

Reputation: 415

Is preserving all functional dependencies after decomposition of a relation required?

After converting a relation to BCNF, if a functional dependency(FD) applicable on original schema is lost, a new 'redundant' table is created in order to preserve all original FD's,if possible.I understand FD's are important for decomposition, but what is their use after decomposition? Why must we try to preserve all the FD's? Does it really matter if one or two FD's are lost after converting a relation to BCNF?

Upvotes: 1

Views: 585

Answers (1)

reaanb
reaanb

Reputation: 10065

FDs are used for both derivation and constraint. A -> B means we can get B given A, and that we'll only get one B for each A. If we lose that FD, we can no longer determine a single B from A. If we translate A and B into business domains, e.g. Customer and Address, it should be clear how the loss of an FD can lead to practical problems.

Upvotes: 2

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