Cardinality is the number of occurrences of one object that can be related to the number of occurrences of another
cardinality can be expressed as one or many
Example: A parent can have many children
but a nation can have only one president
Modality is 0 if the occurrence of relationship is optional and it is 1 if occurrence of relationship is mandatory
Example: For any order there must be a customer
but it is not necessary that the order is processed
