If relation is decomposed into and the decomposition is said
If a relation R is decomposed into R1 and R2, the decomposition is said to be lossless if:
- A.
R1∩R2 is a superkey for R1 or R2.
- B.
R1∪R2 is a superkey for R1 or R2.
- C.
R1∩R2 is a superkey for R1 and R2.
- D.
R1∪R2 is a superkey for R1 and R2.
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Correct answer: A
A decomposition of R into R1 and R2 is lossless if the intersection of R1 and R2 (i.e., R1∩R2) forms a superkey for at least one of the original relations R1 or R2.
Lossless Join Condition: R1∩R2→R1 or R1∩R2→R2
This means the common attributes between R1 and R2 must uniquely identify all attributes in at least one of the relations.