Suppose we have a relation R(A, B, C) with the FD A -> B. Let's say that, for two tuples t and u in R, if both t[C] and u[C] satisfy a boolean condition - say less than a constant C - then t[B] = u[B]. Does this constitute a functional dependency?
On a more practical sense, how to normalize this relation and eliminate the clear redundancy in R(A, B, C) and allow for lossless joins?
let R be Person(id,age,drivers_licence_number)
let the condition be age<5
Clearly drivers_license_number is not functionally dependent on age, since two Persons with the same age have different drivers_license_numbers. But no person with age<5 has a drivers_license_number.
Because the relationship is not a functional dependency, splitting this relation wouldn't be a normalization.
