Consider the universal relation r= {a, b, c, d, e, f, g, h, i, j} and the set of functional dependencies f.
f = {{a, b} _{c, d},
{d}=> {e, f, g},
{f, g}_{h},
{a}+{i},
{a, b} {e, g},
{a, i} + {i, j}}
(a) what is the closure of the set {a, d}?
(b) what is the key for r?
(c) what is the minimum cover for the set of functional dependencies f?
(d) decompose r into 2nf.
(e) decompose r into 3nf.

Explain the circumstances for which the interquartile range is the preferred measure of dispersion. what is an advantage that the standard deviation has over the interquartile range? choose the correct answer below. a. the interquartile range is preferred when the distribution is symmetric. an advantage of the standard deviation is that it increases as the dispersion of the data increases. b. the interquartile range is preferred when the data are not skewed or no have outliers. an advantage of the standard deviation is that it uses all the observations in its computation. c. the interquartile range is preferred when the distribution is symmetric. an advantage of the standard deviation is that it is resistant to extreme values. d. the interquartile range is preferred when the data are bell shaped. an advantage of the standard deviation is that it is resistant to extreme values. e. the interquartile range is preferred when the data are skewed or have outliers. an advantage of the standard deviation is that it uses all the observations in its computation. f. the interquartile range is preferred when the data are bell shaped. an advantage of the standard deviation is that it increases as the dispersion of the data increases.