You know EM Relational Diagrams, right? Well, in class, he asked us to draw one for a hospital, which had patients matched with tests/examinations matched with doctors. I had a scheme which used three tables - Patients, Exams, and Doctors. Each exam was matched many to one to each of a doctor and a patient, since each patient has many tests, each test can have different doctors, and each doctor can administer different tests. But he argued that I should have only had two tables, Patients and Doctors, connected the two of them and had examinations as an attribute of Doctors or something. It made absolutely no sense, and I still think he's patently wrong -- which is why I drew my schema on the test.