Question

Consider the situation where entity E₁ and E₂ are connected by a one-to-one relationship R. Choose all the TWO correct answers from the following list so the chosen answers can describe how to transform E₁, E₂ and R into a relational schema diagram _________________________.

1. create a table T₁ for E₁ and create a table T₂ for E₂.
2. create a table T for either E₁ or E₂, but no need to create two tables as described in answer (a).
3. create only one table T₁₂ which contains both E₁ and E₂.
4. create a table T_R for R to describe the one-to-one relationship between E₁ and E₂.
5. no need to create a table for R, but have to append a foreign key in T₁ which points to T₂.
6. no need to create a table for R, but have to append a foreign key in T₂ which points to T₁.
7. no need to create a table for R, but have to append a foreign key in both T₁ and T₂, which points to each other.
8. no need to create a table for R, and a foreign key can be appended into either T₁ or T₂.
9. no need to create a table for R, but where to append the foreign key depends on the details of the one-to-one relationship.

Answer 1

Here the relationship between E1 and E2 is one to one.

For converting one to one relationship, either key of one entity can be added as foreign key in to schema of other entity.

Also for both the entity, one table will be created for each entity. So total #of table we have is 2 where one table contains primary key of other entity.

If participation of both the entity is total then either entity's key can be selected to be placed as foreign key into other. If participation of suppose E1 is total, then include primary key of E2 into E1 is preferred. No compulsion though. Here since nothing is mentioned about participation, either entity can be chosen.

So the correct option is:

no need to create a table for R, and a foreign key can be appended into either T1 or T2.

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