However, if the minimum cardinality on one side is 0, then make the other relation the
parent. For instance, if there were a 1:1 relationship between ???Room??? and ???Projector???, but not all rooms had
projectors, you would make the Room relation the parent, and put a foreign key column in the Projector
relation. This will be more space-efficient, since you will have a foreign key field only when there is a Projector
tuple to associate with a Room tuple.
For 1:N relationships, the relation on the 1 side will be the ???parent,??? and the relation on the N side will be
the ???child.??? All one must do is add a foreign key column to the child relation so that the ???many??? children can
be related to the ???one??? parent entity. For instance, to implement the advisor/advisee relationship, simply add
a foreign key column to the Student relation, name the foreign key column ???FacultyAdvisor???, and prepare to
populate the column with values of the primary key of the Faculty relation.
Many-to-many relationships are more complex. To implement an N:M relationship, one must create a new
table, a new relation. Such a relation is sometimes called an intersection table or a relationship relation. The
intersection table includes foreign key columns for both entities in the relationship.
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