Reference fields are pretty special in ServiceNow. They let you link two records, letting you associate things such as which room you just checked in to. It represents a relationship that makes sense for your data.
Almost every reference field uses
sys_id values to join records. But you do have the power to specify another field, by populating the Reference key in the advanced settings of the dictionary. This requires careful consideration for it to make sense, though.
Relationships change, though. Wouldn't it be great to create the other side if needed? And clear up broken links when one side goes? At least in ServiceNow, this is possible.
What happens if you try to associate with a record that ...