This is a long overdue followup to 2016’s “URLs and DOIs: a complicated relationship”. Like that post, this accompanies my talk at PIDapalooza, the premier festival of PIDs (Persistent Identifiers). I don’t think I need to give a spoiler warning when I tell you that it’s still complicated. But this post presents some vocabulary to describe exactly how complicated it is. Event Data has been up and running and collecting data for a couple of years now, but this post describes changes we made toward the end of 2018.