preliminary definitions
- Functional Dependencies
- Let R be a relation variable, and let X and Y be arbitrary subsets of the set of attributes of R. Then we say that Y is functionally dependent on X--in symbols,
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- (read ¡°X functionally determines Y,¡± or simple ¡°X arrow Y¡±) - if f, in every possible legal value of R, each X-value has associated with it precisely one Y-value.
- Trivial dependency
- the right-hand side is a subset ( not necessarily a proper subset ) of the left-hand side.