Third Normal Form A relation schema R is in third normal form(3NF)if for all: oa-→BinF+ at least one of the following holds: o→B is trivial(i.e.,B∈o) a is a superkey for R Each attribute A in B-a is contained in a candidate key for R. (NOTE:each attribute may be in a different candidate key) If a relation is in BCNF it is in 3NF(since in BCNF one of the first two conditions above must hold). Third condition is a minimal relaxation of BCNF to ensure dependency preservation (will see why later). Database System Concepts-5th Edition,Oct 5,2006 7.20 @Silberschatz,Korth and SudarshanDatabase System Concepts - 5 7.20 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Third Normal Form A relation schema R is in third normal form (3NF) if for all:  →  in F+ at least one of the following holds:  →  is trivial (i.e.,   )  is a superkey for R Each attribute A in  –  is contained in a candidate key for R. (NOTE: each attribute may be in a different candidate key) If a relation is in BCNF it is in 3NF (since in BCNF one of the first two conditions above must hold). Third condition is a minimal relaxation of BCNF to ensure dependency preservation (will see why later)