actually if you don't mind, I was wondering if the third table was actually a list of unique cars (so no repeats) then it would be a one to many relationship. I think I understand I would define a new relationship table for many-to-many relationship, but if it's one to many relationship and "size" is an attribute of "cars" then maybe "idSize" should be inserted back into table, "Cars"? Sorry if that is confusing.