What is the difference between a binary relationship that exhibits a 1:1 cardinality constraint and a binary relationship

QUESTION:

What is the difference between a binary relationship that exhibits a 1:1 cardinality constraint and a binary relationship that exhibits a 1:n cardinality constraint?

SOLUTION

In a binary relationship that exhibits a 1:1 cardinality ratio, each occurrence of entity type E1 is associated with at most one occurrence of entity type E2 and vice versa. In a binary relationship that exhibits a 1:n relationship, each occurrence of entity type E1 is associated with, at once, n occurrences of entity type E2, while each occurrence of entity type E2 is associated with, at most, one occurrence of entity type E1.