A college course may have one or more scheduled sections, or may not have a scheduled section. Attributes of COURSE include Course_ID, Course_Name, and Units. Attributes of SECTION include Section_Number and Semester_ID.
Semester_ID is composed of two parts: Semester and Year. Section Number is an integer (such as "1" or "2") that distinguishes one section from another for the same course but does not uniquely identify a section.
How did you model SECTION?
Why did you choose this way versus alternative ways to model SECTION?