This (fantastic) paper is cited in the Google Megastore paper [1] and we actually use the term "entity group" in our product [2] indirectly because of it. Pat Helland is always worth reading; thanks to the submitter for the reminder.
[1] https://static.googleusercontent.com/media/research.google.c...
[2] https://cloud.google.com/datastore/docs/articles/balancing-s...