How would I draw an ERD for a situation like this:

professors can teach the same course in several semesters, and each offering must be recorded.

If I know that:

Professorss can have an SSN and courses can have a courseid.

Any helpful suggestions are welcome.

We'd be happy to help, but we don't want to do all the work for you. Can you show us what you have so far?

To help you out, four entities should be sufficient to track the information in your post.

Here is your data dictionary:

[B]Staff[/B]
    SSN (Primary Key)
    Other staff data

[B]Course[/B]
    CourseID (Primary Key)
    Other Course Data

[B]TaughtCourse[/B] (this is important, you need a link table)
   CourseID (Foreign Key)
   SSN (Foreign Key
   Other details (e.g when, where, notes)

The link table is needed as you cant basically have a many to many relationship between staff and courses. It just doesnt work like that.

In my example, one Staff can have many TaughtCourse (one staff member can teach many groups) and each Course may be taught many times to many different groups. However, one group can only be a part of oe course.

So its a ONE staff <- may teach -> MANY TaughtCourse
and ONE ToughtCourse < - can have -> MANY Course

commented: Great!!! (^ - ^) +1

Thanks jbennet, I had something similar in mind.

Another thing, how would I encorporate an employee(business staff) processing a transaction to a situation where you have a client purchasing an item from a member the company's production staff?