I'm creating a course enrollment system and have a question about the domain model I've designed thus far. A central domain class is Course, which represents a unique course offering (e.g. Intro to Psychology, Advanced Calculus). The Seminar class represents a scheduled instance of a Course (e.g. Intro to Psychology-2nd Semester, MWF 1:00-2:00pm). I modeled these classes as Associations (Courses will have 1..n Seminars). This seems right, but I can see how it might be argued (weakly IMO) that this an Inheritance relationship. After all, isn't a Seminar a specialized type of Course?