Relational Model 2. Consider the relations Students, Faculty, Courses, Rooms, Enrolled, Teaches, and Meetsin defined below. Students(sid: string, name: string, login: string, age: integer, gpa: real) Faculty(fid: string, fname: string, sal: real) Courses(cid: string, cname: string, credits: integer) Rooms(rno: integer, address: string, capacity: integer Enrolled(sid: string, cid: string, grade: string) Teaches(fid: string, cid: string) Meets Incid: string, rno: integer, time: string) a) List three foreign key (to primary key) constraints among these relations. b) Give three examples of tuple or domain constraints over these relations that are not primary key or foreign key constraints. For each of your constraints in (a) and (b), describe in one sentence why your constraint is necessary