How to get the relationship between backup set?
From SQL:

SELECT p.start_time, p.handle, p.tag, s.backup_type, 
       s.incremental_level, controlfile_included
FROM   v$backup_piece p, v$backup_set s
WHERE  p.set_stamp = s.set_stamp
AND    p.set_count = s.set_count
ORDER BY tag;


For the backup type: 

L: Archived Redo Logs
D: Datafile Full Backup (or control file backup or autobackup)
I: Incremental Backup 


You can see which files are in each backup by the TAG column.  

Keep in mind that this view may report backups are don't actually exist on disk unless you:

RMAN&gt; crosscheck backup;
RMAN&gt; delete expired backup;


Refer to the Oracle Database 12c Documentation (or whatever version of Oracle you are using) for more information: 

v$backup_set

v$backup_piece