How would you approach Exercise 4.4.1 in A First Course in Database systems, by Jeff Ullman 3rd edition? I don't see how weak entity sets could be involved here... If every student has a student ID, and every course has a unique course number, then there is no need for a weak entity set! Also, is it possible for two entity sets to be connected by another entity set rather than a relationship?

double diamond Example 4.23: In Fig. 4.22, the relationship Studio-of need not be a support- ing relationship for Contracts. The reason is that each movie has a unique own- ing studio, determined by the (not shown) many-one relationship from Movies to Studios. Thus, if we are told the name of a star and a movie, there is at most one contract with any studio for the work of that star in that movie. In terms of our notation, it would be appropriate to use an ordinary single diamond rather than the double diamond, for Studio-of in Fig. 4.22. D 4.4.4 Exercises for Section 4.4 Exercise 4.4.1 One way to represent students and the grades they get in courses is to use entity sets corresponding students, to courses, and to "en to rollments." Enrollment entities form a "connecting" entity set between students and courses and can be used to represent not only the fact that a student is taking a certain course, but the grade of the student in the course. Draw an E/R diagram for this situation, indicating weak entity sets and the keys for the entity sets. Is the grade part of the key for enrollments? 4.4.2 Modify your solution to Exercise 4.4.1 so that we can record grades of the student for each of several assignments within a course. Again, indicate weak entity sets and keys