Page "Database normalization" Paragraph 13

* There are circumstances in which certain facts cannot be recorded at all.

For example, each record in a " Faculty and Their Courses " table might contain a Faculty ID, Faculty Name, Faculty Hire Date, and Course Code — thus we can record the details of any faculty member who teaches at least one course, but we cannot record the details of a newly hired faculty member who has not yet been assigned to teach any courses except by setting the Course Code to null.

This phenomenon is known as an insertion anomaly.