What are some of the uses of one to one relationships? Provide examples

What will be an ideal response?

A one to one relationship can be used to separate data that must be secured from more public data. For instance, an Employee table could be split into two tables. One would contain the general, publicly available information about an employee and the other would contain private information such as his or her social security number, number of tax exemptions, etc. Another use is to create a hierarchy of tables in order to prevent unavoidable null attributes. If one had a Vehicle entity, for example, that contains data about several kinds of vehicles each with their own attributes, one could create a separate entity for each kind of vehicle with a one to one relationship to the original vehicle entity. This would eliminate nulls in the vehicle table for attributes not related to a particular kind of vehicle.