Lossless Join Decompositions
Decomposition of R into X and Y is lossless-join w.r.t. a set of FDs F if, for every instance r that satisfies F:
It is always true that r (r) |?| (r)
- In general, the other direction does not hold! If it does, the decomposition is lossless-join.
Definition extended to decomposition into 3 or more relations in a straightforward way.
It is essential that all decompositions used to deal with redundancy be lossless! (avoids Problem 2, previous slide)