A doctor can be scheduled for many appointments, but may not have any scheduled at all. Each appointment is scheduled with exactly 1 doctor.
A patient can schedule 1 or more appointments. One appointment is scheduled with exactly 1 patient. An appointment must generate exactly 1 bill, a bill is generated by only 1 appointment.
One payment is applied to exactly 1 bill, and 1 bill can be paid off over time by several payments. A bill can be outstanding, having nothing yet paid on it at all. One patient can make many payments, but a single payment is made by only 1 patient.
Some patients are insured by an insurance company. If they are insured, they can only carry insurance with one company. An insurance company can have many patients carry their policies. For patients that carry insurance, the insurance company will make payments, each single payment is made by exactly 1 insurance company.
You will probably have to add attributes to entities, like in the following exemplesRemember : CREATE TABLE syntax
CREATE TABLE DOCTORS ( doc_id integer NOT NULL, doc_firstname varchar(255) NOT NULL, doc_lastname varchar(500) NOT NULL );
DROP (REMOVE) COLUMN
ALTER TABLE DOCTORS ADD COLUMN "bdate" DATE;
ALTER TABLE DOCTORS DROP COLUMN bdate;
ALTER TABLE DOCTORS ADD COLUMN "newCol" DATE; UPDATE DOCTORS SET newCol = bdate;
ALTER TABLE ONLY DOCTORS ADD CONSTRAINT doc_pk PRIMARY KEY (doc_id);
ALTER TABLE ONLY APPOINTMENTS ADD CONSTRAINT fk_doc FOREIGN KEY (f_doc_id) REFERENCES DOCTORS(doc_id) ON DELETE SET NULL;
ON DELETE SET NULL meaning that if a doctor is deleted, then the appointment remains with null in the f_doc_id field