Decomposition in Relation

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Decomposition:
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Let R be a relation schema
A set of relation schemas { R1, R2,…, Rn } is a decomposition of R if
  • R = R1 U R2 U …..U Rn
  • Each Ri is a subset of R ( for i = 1,2…,n)


Lossy Decomposition:

When union of R1UR2UR3.......Rn is taken and output obtained from this does not match with original relation schema i.e. R that means there is loss of information and such type of decomposition is called as lossy decompostion.


Lossless Decomposition :

 A decomposition of {R1,R2,R3,.............Rn} of a relation R is called a lossless decomposition is R is natural join of R1,R2.........Rn produces exactly relation R.




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