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The Relational Database Dictionary, Extended Edition by C. J. Date

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Chapter 7. F

FALSE See BOOLEAN.

FD Functional dependency.

FD implied by a superkey The FD A B is implied by a superkey if and only if A is a superkey for the pertinent relvar.

FD preservation Decomposing a relvar R into its projections R1, R2, . . ., Rn in such a way that FDs are preservedthat is, every FD satisfied by R is implied by those satisfied by R1, R2, . . ., Rn. R1, R2, . . ., Rn here are said to be independent projections. Note: Projections that aren't independent are said to be interdependent, not dependent. See also atomic relvar.

Example: Suppose relvar S satisfies the additional FD {CITY} {STATUS}; i.e., the status for a given supplier is a function of that supplier's location. Then replacing S by its projections on {S#,SNAME,CITY} ...

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