What is Cardinality of a Relation?

Cardinality is the degree of relationship. It is the number of occurrences in one entity to the number of occurrences in another entity of a data relationship.
There are three degrees of relationship, known as:
one-to-one (1:1)
one-to-many (1:M)
many-to-many (M:N)

What is the cardinality and existence of each of the following relationships in just the direction given?
State any assumptions you have to make.

Husband to wife
Student to degree
Child to parent
Player to team
Student to course
Citizen to Country

Husband to wife (1:1) OR (1:M)
Student to degree (I:M) OR (N:M)
Child to parent (1:M) (Mother & Father)
Player to team (1:M)
Student to course (1:M)

For each of the following pairs of rules, identify two entity types and one relationship. State the cardinality of the relationship in each case and draw ER Diagram.

• A department employs many persons.
• A manager manages one department.
• An author may write many books. A book may be written by many authors.
• A team consists of many players. A player plays for only one team.
• A lecturer teaches, at most, one course. A course is taught by exactly one lecturer.
• A flight connects two airports. An airport is used by many flights.
• A purchase order may be for many products. A product may appear on many purchase orders.
• A customer may submit many orders. An order is for exactly one customer.

Draw an ER diagram and indicate the cardinality for each relationship.