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Let r be a relation instance with schema R = (A, B, C, D). We define $r_1 = \pi_{A, B, C} (R)$ and $r_2=\pi_{A, D} (r)$. Let $s =r_1 \: * \: r_2$ where $*$ denotes natural join. Given that the decomposition of $r$ into $r_1$ and $r_2$ is lossy, which one of the following is TRUE?

  1. $s \subset r$

  2. $r \cup s =r$

  3. $r \subset s$

  4. $r*s=s$

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5 Answers

–4 votes
–4 votes
(a) (b) and (d)

Reason:

obviously c(r cannot be a subset of s, since r1 and r2 are lossy decomposition) not true

a should be true(since s cant have values outside r)

d(natural join takes common element) since a is true
Answer:

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