University ER
We have both students and instructors are associated with departments. Notice that we've got a double line from instructor to instructor department and then an arrow from there to department which is saying that every instructor is in exactly 1 department.
A student has at most one instructor as their advisor.
We have several different different sections of that course. They're all going to have in common title and credits. So that information belongs with the course, but we want to separate out the idea of particular instances of this course, so we'll have a separate weak entity set that is associated with courses.
When a student registers or takes something, we want to record, not just that a student took CS6O83, but that they took section A, spring semester, 2023. So that's what this "takes" relationship set is doing between students and sections. When a student completes taking the course, they'll get a "grade". Similarly, we're going to keep track not just of the fact that a particular professor taught a course, but we want to keep track of which particular sections they taught.
There are other things about sections like when is the section offered, so it would be in a particular "time_slot" and what "classroom" is it in and so forth.
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