ERD-esque problem--need a content type that only nodereferences others?

I'm trying to create some related content types: Class Description, Location, and Class Session. Our organization has classes that offer the same content (e.g. "How to Bake a Cake") at different locations (e.g. "Classroom A" and "Classroom B") and times. The Description contains a few paragraphs about what the class covers, which is the same for every instance of the class, and each Location has its address and so forth.

As an experiment, I successfully created content types for Description and Location, using a nodereference for location and a datetime field that can repeat. So I can say that "How to Bake a Cake" takes place in "Classroom B" at noon on Friday and at 4pm on Monday, and I can make those meetings appear separately on a calendar.

The problem is that any given class might be taught in different locations as well as at different times. So I think I need another entity, Class Session, which refers to both the Class Description and the Location. Class Session would only consist of two nodereferences (description, location) and one datetime field. It doesn't need its own title or body, because those can come from Class Description--they're the same for every session/instance of the class.

The problem comes when I try to create the Class Session content type--it seems like title and body are required. I'm sure problems of this structure are common, so is there some good way to work around it?