Simulating an enum field

I'm a newbie to FMP6, so I hope I haven't missed the answer when searching!

I want a field that holds a serial number but displays as a text string. For example, the field Students:course contains an ID number relating to a record in Courses:courseID, but displays as Courses:courseName. [Hopefully my pseudo-syntax is clear? Database:fieldName]

In edit mode, Student:course should produce a pop-up list or menu of all Courses:courseName, and plug the corresponding Courses:courseID. In display mode, it should display Courses:courseName based on the courseID that's actually stored.

I know about creating dynamic value lists for formatting that would display ID and text together, but once the choice is made, the ID displays.

I'm sure this is a common problem, and I hope I've described it sufficiently to jog memories. I don't want to rely on courseName itself as a relational key, since it should be editable without breaking existing relationships.

Thanks so much,

Chap