Relationship Cardinality is indicated by the presence of numbers on either end of the relationship line connecting the Classes.

0..* indicates that the cardinality is may be related to one or more instance of the class
0..1 indicates that the cardinality is may be related to one and only one instance of the class
1..* indicates that the cardinality is must be related to one or more instance of the class
1 indicates that the cardinality is must be related to one and only one instance of the class

An example of Relationship Cardinality in diagrams is given below: