ER Model

Question

The relationship between 2 entity A and B is 1:1 and the relationship is optional at the end . Only 50% of B entities are related To A .

Now Consider mapping these entity types into relations 

Select the best statement :

A ) A and B should be seperate and foreign key should be in A relation 

b) A and B should be seperate and foreign key should be in B relation 

c)  A and B should be seperate and foreign key should be in A and B both relation 

d) None of these 

Verify please

Comments

is it option A?

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The Answer should be  B) 

Since we have 50% of the entities of B related to A and A&B are seperate we can use a foreign key should be in B relation   to refer A.

What is answer given ???????

Answer 1

d) none of these

because we are not sure about A's participation may be the relation will merged into A or B

it cant be decided

Answer 2

Given relationship as 1:1 and 50% of B entities are related to A. A is related to those 50% only in 1:1 cardinality . So there must be a way to map the relation between A nd B . Bring an attribute from B to A so that A should relate to those 50% . Option A is correct.

Why option B is not best because what if B has foreign key ? there will be 50% of wastage by making null values. That A is not related to B