Is the following statement regarding triviality of functional dependencies true or false? α → β is trivial if β ⊆ α True False
QUESTION 7
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Is the following statement regarding triviality of functional dependencies true or false?
α → β is trivial if β ⊆ α
True
False
QUESTION 8
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The next best alternate after BCNF is 3NF. We can say that this schema is 3NF but not BCNF. Match the following statements that make this 3NF and not BCNF
dept_advisor(s_ID, i_ID, dept_name)
§ With function dependencies:
i_ID → dept_name
s_ID, dept_name → i_ID
§ Two candidate keys = { s_ID , dept_name }, { s_ID , i_ID }
- A. B. C. D. i_ID is not a superkey
- A. B. C. D. { dept_name} – {i_ID }
- A. B. C. D. dept_name is contained in a candidate key
- A. B. C. D. s_ID, dept_name
A. superkey
B. {dept_name }
C. dept_advisor is not BCNF
D. Since each attribute A in β – α is contained in a candidate key for R, dept_advisors is 3NF
QUESTION 9
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How do we calculate a functional dependence closure? Which of the following give a good example of the process?
add non-candidate keys to the dependencies, e.g. F + non-key attribute
found unidentified dependencies, if a-->b and a-->c, then b-->c is a functional dependency
get all the inferred dependencies: if a --> b and b--> c, then we can infer a --> c is a functional dependency
all the superkey dependencies should be calculated, e.g. F + (b-> Super Key)
QUESTION 10
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Choose disadvantages of 3NF compared to BCNF
Redundancy
Can lead to the necessity of null values
Lossy
Bad Form
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