The elements of the domain of an attribute may be ordered pairs of values. True False0.5 pointsSome relations may not have a foreign key. True False0.5 pointsA foreign key in a relation should consist of exactly one attribute. True False0.5 pointsA foreign key in a relation R can NOT be used to refer to tuples in R itself. True False

A key of a relation may have more than one attribute. True False

The foreign key can be used to identify a specific record of data in a relational database.1 pointTrue False

Which of the following is wrong about domains of a relation?Question 29Select one:a.Two or more attributes can be defined on the same domainb.Two attributes that include values from different domains can easily be comparedc.A tuple can draw values from different domainsd.A pool of atomic values constitutes a domain

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

__________ is a specific domain in the relation which has entries of all tuples.