36. Suppose we label the attributes R of a relation by integers [1..N] and repla

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36. Suppose we label the attributes R of a relation by integers [1..N] and replace "visit(S)" in the program in Problem 35 by "if (closure(S) is RI output(S), return; )". Then the output consists of a. all the superkeys in the relation. b. all the keys in the relation. c. a subset of superkeys that includes all the keys. d. a subset of keys that includes all superkeys 37. Finding all the keys in a relation is necessary in 3NF decomposition because a. b. c. d. in some cases we need a key to be a decomposed relation we need to check if the right side of an FD is part of a key. we need to know if the left side of an FD is a key we need to project the FDs onto the decomposed relations 38. As part of BCNF decomposition, we need to project the FDs onto the two decomposed relations in each recursive step. Enumerating all subsets X of the attributes R' in each of these relations is needed because an FDX->B may be set for R' where B is a. closure(x)-X. b. the union of closure(X) X and R'. c. the intersection of closure(X)-X and R' d. the difference between R' and closure(X) - X. 39. In each recursive step of 4NF decomposition, we may have to test every possible FD and MVD for each of the decomposed relations. We need set enumeration for both left and right sides of each possible MVD to perform a chase test. However, we can skip a subset as the left side if a. b. c. d. it does not contain the left side of any given dependency it is not a subset of the left side of any given dependency. it does not contain the right side of any given dependency. it is not a subset of the right side of any given dependency.

Explanation / Answer

Hi,
This one has multiple questions, which is against chegg policy, please post others are separate question and we would be happy to assist you,
Answering 37th, as 36th has 35 as dependency and 35 is not given,
37.A relation is in 3NF if transitive dependency is not there i.e. no non prime attribute should be determined by another non prime attrbute,
since we need to know if every deriving attribute is key, we need to first find all key or prime attributes, hence the option C is correct,
option B is incorrect, because we are not worried about the derived attributes but about prime attributes,
option A is false, as we can decompose without keys

Thumbs up if this was helpful, otherwise let me know in comments

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