Process-Synchronization
October 11, 2023
Software-Engineering
October 12, 2023
Process-Synchronization
October 11, 2023
Software-Engineering
October 12, 2023

Database-Management-System

Question 102

Let r be a relation instance with schema R = (A, B, C, D). We define r1 = ΠA,B,C(R) and r2 = ΠA,D(R). Let s = r1*r2 where * denotes natural join. Given that the decomposition of r into r1 and r2 is lossy, which one of the following is TRUE?

A
s ⊂ r
B
r ∪ s = r
C
r ⊂ s
D
r * s = s
Question 102 Explanation: 
Let us consider an example:
Table r: R(A, B, C, D)

Table r1: ΠA,B,C(R)

Table r2: ΠA,D(R)

S = r1 * r2 (* denotes natural join)
Table S:

Table r ⊂ Table S
⇒ r ⊂ S
Correct Answer: C
Question 102 Explanation: 
Let us consider an example:
Table r: R(A, B, C, D)

Table r1: ΠA,B,C(R)

Table r2: ΠA,D(R)

S = r1 * r2 (* denotes natural join)
Table S:

Table r ⊂ Table S
⇒ r ⊂ S
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