JSON:API — Latest Specification (v1.1) and Links Object Clarification Needed
The relationship is given meaning is given by the name of the relationship (e.g. author or comments in the example on the spec home page). The “related” link points to the related resource; the self link points to the “join” between the current resource and the related resource (similar to a foreign key in database terms).
They don’t, they’re for use in collections