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## Explain lossless join property. Database Management Systems - 10CS54 VTU notes (Dec /Jan 12/Jan 2016)

Explain in brief?By:anonymousguy7799

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## Answers

Lossless (Non-additive) Join Property of a Decomposition: Definition: Lossless join property: a decomposition D = {R1, R2, ..., Rm} of R has the lossless (nonadditive) join property with respect to the set of dependencies F on R if, for every relation state r of R that satisfies F, the following holds, where * is the natural join of all the relations in D: * (π R1(r), ..., πRm(r)) = r Note: The word loss in lossless refers to loss of information, not to loss of tuples. In fact, for “loss of information” a better term is “addition of spurious information” Algorithm 11.1: Testing for Lossless Join Property Input: A universal relation R, a decomposition D = {R1, R2, ..., Rm} of R, and aset F of functional dependencies. 1. Create an initial matrix S with one row i for each relation Ri in D, and one column j for each attribute Aj in R. 2. Set S(i,j):=bij for all matrix entries. (* each bij is a distinct symbol associated with indices (i,j) *). 3. For each row i representing relation schema Ri {for each column j representing attribute Aj {if (relation Ri includes attribute Aj) then set S(i,j):= aj;};}; (* each aj is a distinct symbol associated with index (j) *) Algorithm 11.1: Testing for Lossless Join PropertyNikhil-bharadwaj

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