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?
1
S1 is true and S2 is false.
2
Both S1 and S2 are true.
3
Both S1 and S2 are false.
4
S1 is false and S2 is true.