Functional dependency

Question

Comments

which exam this question came?

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Not of any exam question

This is workbook question

Answer 1

Answer should be D,

Because R relation is decomposed into R1 and R2 ,then relation should be lossless join .for lossless decomposition ,there should be two conditions

(1) every attribute of R must be in$  R_1,R_2$  ( $R_1 $\Join$ R_2$ $ \cong$ R)

(2)($R_1\cap R_2$)$\rightarrow$ $R_1$

           //($R_1\cap R_2$) is super key of $R_1$

                       (OR)

        $(R_1\cap R_2)\rightarrow R_2$

             //$(R_1\cap R_2) $ is super key of $ R_2$

Otherwise when we join R1 and R2 ,there will be spurious tuple(unwanted tuples) in relation.so decomposition should be based on superkey.