explain?

Question

R is relationship with 1 : 1 cardinality, 30% participation at E1 end 70%
participation at E2 end which is the best possible design?
a. E1 and E2 kept separate with foreign key at E1 end
b. E1 and E2 kept separate with foreign key at E2 end
c. E1 and E2 kept separate with foreign key at E1 as well as E2
d. E1 and E2 merges into a single table with no foreign key

Comments

Weird. 1:1 cardinality implies every entity from E1 has atmost one entity from E2 in relationship R. If 30% participate from E1 then only 30% should participate from E2 also; because every $e \in E1$ has one and only one $f \in E2$. So the question itself seems wrong. But I guess this is one of those questions that make sense in the “GATE universe.” :P

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@ytheuyr Here no. of participation from E1 and E2 is not given. Only % is given. That means 30% of total tuples from E1 side will be equal to 70% of total tuples from E2 side as 1:1 mapping. So, question seems correct to me.

Answer 1

To me I think now

Because of 1 to 1 mapping it can merges into a single table . No need for FK .If we do then we have a problem to select primary key . So , E1 and E2 kept separate , and we will foreign key at E2 because 70% participation at E2 ,because of that null value at E2 will be less .

In case of E2 if i choose foreign key at E1 then participation at E1 30% , so the Null values will be increased .

Option B is correct .

I might be wrong but to me i think I`m right :P .

Comments

ACTUALY correct option is(B) but i don't know how.?? 

yes  , it is true that in one to one cardinality  we can merge the table ! but they said participation from R is 70% and from another entity is 30%, so i want to know that if we combine the table than we can make primary key from that table which is more in participation and foreign key from another table..

so i think(b) option should be like this:

E1 and E2 merged with foreign key at E2 end

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so wt is concept that we are not are not merging the table.?? is it that  we need total participation to decide from atleast one end.?? to have primary key.??

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@Pranay Datta 1 @focus _GATE

In 1 to 1 mapping we merge tables when we have full participation on both sides. Here we put foreign key on E2 side (70% participation) because this will produce less NULL values compared to when we put foreign key on E1 side (30% participation).