Suppose A is a foreign key in R that refers to tuples of S using values of the key attribute B of S. Let X be the set of all non-null values of    column A and let Y be the set of all values of column B. Identify the correct relationship between X and Y that holds in    all instances of R and S: X is a subset of Y X is a proper subset of Y Y is a subset of X X need not be a subset of Y and Y need not be a subset of X

The correct relationship between X and Y that holds in all instances of R and S is: X is a subset of Y.

Here's why:

A foreign key in a table is a key from another table that is used to maintain the relationship between the two tables. The table that contains the foreign key is called the referencing table or child table, and the table that is referred to by the foreign key is called the referenced table or parent table.

In this case, A is a foreign key in table R that refers to tuples of table S using values of the key attribute B of S. This means that every non-null value of A (which forms set X) must correspond to a value of B (which forms set Y).

Therefore, all values in X must also be in Y, making X a subset of Y. However, Y may contain values that are not in X, so it's not necessarily true that Y is a subset of X.

So, the