DBMS Grand Test 1 Question51

+1 vote

Consider the folowing entity relation diagram

Below are three possible relationships set for this entity relation diagram

1
A B C D
a1 b1 c1 d1
a1 b1 c1 d2
2
A B C D
a1 b1 c1 d1
a1 b1 c2 d2
  3
A B C D
a1 b1 c1 d1
a1 b2 c1 d1

Assume that different symbols stand for different values. which of the above could not be the relationship set for the entity relation diagram ?

(A) 1 only

(B) 1 and 2 only

(C) 2 only

(D) 1, 2 and 3 only

asked Sep 10, 2016 in DBMS by getgatebook (36,850 points)
reshown Dec 24, 2018 by getgatebook

2 Answers

0 votes
Relation 2 should also be invalid since there exist many to one relationships between A and C and B and C whereas according to table 2 it is showing one to many relationship which is inconsistent with the given er diagram. Hence B should be the correct option.
answered Sep 19, 2016 by (1,860 points)
+1 vote

when a relationship's degree is more than binary (ternary and 4-ary....) and there is more than one arraw then in literature it is interpreted in two ways.

1st interpretation: 

Since C has arrow it is interpreted as

for every ABD there is atmost one C  [ ABD \rightarrow C]

Since D has arrow it is interpreted as 

for every ABC there is atmost one D  [ABC\rightarrow D]

2nd interpretation:

Since C, D have arrows, in this interpretation it is interpreted as A\rightarrowC and A\rightarrowD and B\rightarrowC, B\rightarrowD

Since there are two interpretations if you follow first interpretation then Answer is (A) and if you follow 2nd interpretation then it is (B).

Note: Marks are given for A and B

 

 

answered Sep 20, 2016 by getgatebook (36,850 points)
Answer:
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