Litalino can you describe what your actual use case is ?
The data is stored/returned using the JSON:API syntax. The included payload contains the data to populate the various relations. Without the relation, this data is meaningless.
Flarum has helper functions on its JavaScript models to access the relations. For example discussion.user() will return the discussion author. Without other extensions I don't think there are more relations on the discussion. Others are then found on the posts that might have been loaded along with the discussion. Keep in mind relations can return null or undefined on some pages if the relation was not requested when the data was loaded.
