Hello, I was having a look at the ERD provided and case study and was wondering why the Customer subclass has the contactPhoneNumbers[1..3] attribute when in the case study it states: "Each patient or customer is uniquely identified by a client number (N 8) which is assigned to them when they first become associated with the clinic and is used for them thereafter. Also recorded are their name (C), address (A) and one to three contact phone numbers (S 14)."

Hi, Well, you are right this could have been represented as an attribute of the client, but the way it is represented is also not wrong. Right now it is specifically assigned to the customer (who could be a contact person of a patient, and thus we can see that distinction) . Cheers Mehwish