Here is a nice article I found last night. Simon Willison found the SQLite database that Apple Photos uses. It contains photo metadata as well as the aesthetic notation system used by machine learning. In addition, there are digital categories used to label the content of photos. For example, category 2027 is for entertainment, travel, travel, museums, beach activities, etc. I think the quality scores are particularly interesting. There are scores for noise, composition, bright colors, harmonious colors, pleasant lighting / pattern / perspective, and much more. I bet the Apple acquisition of Regaind helped.
Check it out: How to Dig Into the Apple SQLite Photos Database