Top > How to import data > Creating relationships between objects > How to create a relationship
In a one to one relationship you may not wish to overwrite the existing relationship. The best way to discover whether there is one or many objects in a relationship is to attempt to add more than one through the form; if you can add more than one, then it is a one to many relationship. If you cannot add more than one, then it is a one to one relationship.
Example:
You wish to assign Wil Smith as the user to a hardware asset, but only if there is no one already assigned. There can only be one assignment on a hardware asset. You would add Wil Smith as the Reference Instance criteria for the user object in the relationship.