> how to best implement value "Other" for car_model?

Turn the relationship between car_model and car_make itself into a many to many, by adding a car_make_model table. Then relate the car_model(s) to the car_make(s).

This approach would have a single "Other" car_model entry (along with an "Other" car_make entry).

Then by adding an independent primary key to the car_make_model table, rather than using a 'natural' compound key of the make/model ID, you can then link the cars to the car_make_model table (which would then relate the make and model).


Sean