Consider relation R(A,B,C,D,E) with multivalued dependencies:A ↠ B, B ↠ DSuppose R contains the tuples (0,1,2,3,4) and (0,5,6,7,8). Which of the following tuples must also be in R
Question
Consider relation R(A,B,C,D,E) with multivalued dependencies:A ↠ B, B ↠ DSuppose R contains the tuples (0,1,2,3,4) and (0,5,6,7,8). Which of the following tuples must also be in R
Solution
The multivalued dependencies A ↠ B and B ↠ D mean that if two tuples of R agree on attribute A, they must agree on attribute B, and if two tuples agree on attribute B, they must agree on attribute D.
Given the tuples (0,1,2,3,4) and (0,5,6,7,8), we can see that they agree on attribute A (since both have A=0). Therefore, by the multivalued dependency A ↠ B, they must agree on attribute B. But they don't - one has B=1 and the other has B=5.
However, this is not a contradiction, because multivalued dependencies allow for additional tuples to be in the relation. In this case, the tuples that must also be in R to satisfy the multivalued dependencies are (0,1,2,7,8) and (0,5,6,3,4).
These tuples are created by taking the A value from the original tuples (since A is the determinant of the multivalued dependency), and then taking the B and D values from the other tuple (since B and D are the dependent attributes). The C and E values can be from either tuple, since they are not involved in the multivalued dependencies.
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