6.15

Construct an E-R diagram for a hospital with a set of patients and a set of medical doctors. Associate with each patient a log of the various tests and examinations conducted.

---

patientTests is a ternary relationship set.

Another method is, to make the testsAndExaminations entity a weak entity having identifying entity set Patient. And then adding a relationship set between the weak entity testsAndExaminations and MedicalDoctor, representing which medical doctor performed which test and examination. In fact doing that has the added benefit of constraining each entity in testsAndExaminations to a single Patient.

But using a ternary relationship as depicted in the above diagram, also has its benefits. For example, if a group of patients are tested and examined by the same type of test and have the same result, we might associate each of the patients in the group to the same entity in testsAndExaminations.