Relation_5_17

Question

Suppose R(x,y,z) is a relation which satisfy x→ y and S(A, B, C) is a relation that is union compatible with R. Which of the following expressions also satisfy x→ y?

1. R-S     II. S-R     III. S U R     IV. R X S

(A) only I

(B) only I & IV

(C) I, II, III 

(D) II, III, IV

 

Comments

B?

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Ans is B

Bcoz, S-R and S U R will add new tuples which may not satisfy given FD