Appointment: entity or relationship?

A small clinic wants to replace its paper records.

• Patients have a registration number, a name and a date of birth.
• Doctors have an employee code, a name and one specialisation.
• A patient books an appointment with a doctor at a date and time. A
• patient may have many appointments; a doctor sees many patients.
• Each appointment may produce a prescription listing one or more
• medicines with a dosage. A prescription belongs to exactly one appointment
• and means nothing without it.
• Prescriptions are numbered 1, 2, 3 within each appointment.