10.6. Join Dependencies and Fifth Normal Form (5NF)
The anomalies of MVDs and are eliminated by join dependency (JD) and 5NF.
10.6.1. Join Dependencies (JD)
A join dependency (JD) can be said to exist if the join of R1 and R2 over C is equal to relation R. Where, R1 and R2 are the decompositions R1(A, B, C), and R2 (C,D) of a given relations R (A, B, C, D). Alternatively, R1 and R2 is a lossless decomposition of R. In other words, *(A, B, C, D), (C, D) will be a join dependency of R if the join of the join’s attributes is equal to relation R. Here, *(R1, R2, R3, ....) indicates that relations R1, R2, R3 and so on are a join dependency (JD) of R. Therefore, a necessary condition for a relation R to satisfy a JD *(R1, R2,...., Rn) is that
R
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