The minimum cardinality can be zero, one or many. The maximum cardinality can also be zero, one or many. Consider the following example. In most health care clinics the cardinalities would be described as follows. For every instance of the entity patient there will be one or many instances of the entity visit.
Cardinality is bidirectional.
Therefore, we need to determine the relationship from visit to patient also. For each instance of the entity visit there will be one and only one instance of the entity patient. Consider a situation where a health clinic has the option to register a patient before the patient ever visits the clinic. Draw the ERD in the space below. Relationships may also have zero cardinalities.