For large collections of photo/video files, write-access to files is not always available (e.g. located on read-only media).
When trying to rate such files, Diffractor fails.
Please support a database oriented approach to be able to rate read-only files without writing their metadata.
Compare with DigiKam, that has an "internal" database, and can sync both with files themselves, or .xmp files, or its internal database.