Join Dependency
Multivalued Dependencies are helps to lossless decomposition and form relation R
based on trivial multivalued dependencies. An instance, a relation R(A B C) is decomposed
into relation R1(A B) and R2(A C) based on trivial A
? B multivalued functional dependencies.
Join Dependency is helps to lossless decomposition and form relation R based on
nontrivial multivalued dependencies. An instance, a relation R(A B C) is decomposed
into relation R1(A B), R2(B C) and R3(A C) based on nontrivial multivalued functional
dependencies.
Let R = {R1, R2, ..., Rn} be a set of relation schemes over union, the relation r(R)
satisfies the join dependency * [R1, R2, ..., Rn] if r decomposes lossless onto R1,
R2, ... Rn.
That is, r =
pR1(r)
⋈
pR2(r)
⋈
...,
⋈
pRn(r).
A join dependency * [R1, R2, ..., Rn] over R is trivial if it is satisfied by every
relation r(R).
* * * * *
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