Question

Consider the following statements S1 and S2 about the relational data model:
S1: A relation scheme can have at most one foreign key.
S2: A foreign key in a relation scheme $R$ cannot be used to refer to tuples of $R$.
Which one of the following choices is correct?

• A. Both S1 and S2 are true.
• B. S1 is true and S2 is false.
• C. S1 is false and S2 is true.
• D. Both S1 and S2 are false.

Hint:

Self-referencing foreign keys are common in recursive relationships such as organizational hierarchies.

Answer 1

The Correct Option is D

To determine the correctness of statements S1 and S2 regarding the relational data model, let's analyze each statement one by one:

1. S1: A relation scheme can have at most one foreign key.
   • This statement is false. In the relational data model, a relation scheme can have multiple foreign keys. Foreign keys are used to establish relationships between different relations. Each foreign key can reference the primary key of different relations, and so a single relation can have several foreign keys.
2. S2: A foreign key in a relation scheme R cannot be used to refer to tuples of R.
   • This statement is also false. It is possible for a foreign key in a relation scheme R to refer to tuples of R. This is known as a self-referential foreign key, which is often used to model hierarchical or recursive relationships within the same table. For example, in an employee table, a foreign key can be used to represent a supervisor relationship where an employee's supervisor is also another employee in the same table.

Thus, the correct answer is: Both S1 and S2 are false.