The human resources department of a university wants to make sure that every course has exactly one main professor. How can they implement this constraint using the CODASYL framework?

a. They introduce an extra set type called “is-main-professor-of” between record types “professor” and “course”.

b. They introduce an “is-main-professor” record type between record types “professor” and “course” to model the correct relationship.

c. They introduce “main professor” as a data item in the record type “professor”.

d. It is impossible to model this constraint in CODASYL.