 Lossless join decomposition:
 The decomposition of relation R into R_{1} and R_{2} is lossless when the join of R1 and R2 yields the same relation as in R.
 This is also referred as nonadditive decomposition.
 Example:
 The same relation Account figure (a) is decomposed into two relation Acc_Bal and Acc_Branch – as shown in figure (b).
 Now, when these two relations are joined on the common column ‘ano’, the resultant relation will look like Acc_Joined relations as shown figure (c). This relation is exactly same as that of original relation Account.
Account:









Figure (a): An Account relation
Acc_Bal: Acc_Branch:
Ano 
Balance 
A01 
5000 
A02 
5000 
balance 
Bname 
5000 
Vvn 
5000 
Ksad 
Figure (b): Decomposed relation Acc_Bal and Acc_Branch relation
Acc_Joined:
Ano 
Balance 
Bname 
A01 
5000 
Vvn 
A02 
5000 
Ksad 
Figure(c): Joined relation – Acc_Joined relation
 In lossless decomposition, no any spurious tuples are generated when a natural join is applied to the relations in the decomposition.
 In other words, decomposition is lossy if R= join of R_{1} and R_{2}, over X, where R is join is applied to the relations in decomposition.
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