A multi-specialty medical center has several physicians. Each physician has one specialty. The administration of this medical center needs to keep track of the information about each physician such as a physician’s ID, name, specialty, salary, cell phone, etc. The administration also needs to keep track of the information of all patients of this medical center, including patient’s ID, first_name, last_name, date of birth, gender, name of insurance, insurance policy number, telephone, billing address, etc. The administration needs to know which physician takes care of which patients. Assuming each physician takes care of many patients; and a patient may see several physicians with different specialty. Patient must make an appointment to see a doctor. At each appointment when a doctor sees a patient, doctor needs to write a note for this patient which records the date and time he/she sees the patient, purpose of this patient's visit, the treatment or prescriptions or suggestions made for the patient, etc. Some doctors are also involved in one or more research projects with the collaboration of a local medical school. The administration of the medical center needs to know which doctors involved the research project(s), projects' titles, starting time and ending time of each project, and the director of each project. The administration also needs to keep track of doctors’ on-call schedules. Depending on the date, doctors’ on-call hours may be different. When a patient is hospitalized, the administration needs to know the name of hospital, reasons of admission, period of admission, attending doctor, etc.

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