If a dataset contains one or more fields that together can be used to identify some resource in another dataset (or even another instance of the same resource,) those fields taken together make up a “foreign key.” Foreign keys consist of:
The field or fields in the source dataset that make up the key
The target dataset that the key links to
The fields in the destination dataset that should match up to the fields in the source dataset
When a foreign key exists in a dataset, the Observe user interface shows a clickable link to follow they key relationship to the target dataset. You can also use foreign keys to
lookup values from the target dataset by browsing the relations.