Where are back up restore app data guidelines? I am amazed how apple smoothly handles backup &amp; restore application data. Does apple have any guidelines for backup / restore principles? How does applications handle version compatibility of restored data in between different versions of the same app.
iOS Data Storage Guidelines

See Apple's iOS Data Storage Guidelines as a starting point. This documentation is written for developers of iOS applications:


  Overview
  
  iCloud includes Backup, which automatically backs up a user’s iOS device daily over Wi-Fi. Everything in your app’s home directory is backed up, with the exception of the application bundle itself, the caches directory, and temp directory. Purchased music, apps, books, the Camera Roll, device settings, home screen and app organization, messages, and ringtones are backed up as well. Because backups are done wirelessly and stored in iCloud for each user, it’s best to minimize the amount of data that’s stored for your app. Large files will lengthen the time it takes to perform a backup and consume more of a user’s available iCloud storage.


See also the Core Data in iCloud documentation.