Full Answer Section

Natural keys are most commonly used in business information processing because they are easy to understand and use. However, natural keys are not always available, and in some cases, an invented key may be needed.

What is a foreign key? Why are foreign keys used or required in a relational database? Are duplicate foreign key values allowed? Why or why not?

A foreign key is a field or group of fields in a database table that refers to the primary key of another table. Foreign keys are used to establish relationships between tables in a relational database. For example, a customer table might have a foreign key that refers to the primary key of an order table. This would allow us to see which customers have placed orders.

Foreign keys are required in a relational database because they help to maintain the integrity of the data. If a record is deleted from the table that contains the primary key, the foreign key in the other table will be set to NULL. This prevents the foreign key from referencing a record that no longer exists.

Duplicate foreign key values are not allowed because they would violate the referential integrity constraint of the foreign key. The referential integrity constraint ensures that the foreign key value in one table always refers to a valid primary key value in the other table.