@pukkamustard @clacke @how yes, I just heard the same from Mark Graham in IA Slack. He said that it's a Python app (with some cache layers) that sits on top of data in IA storage.
It turns out you can browse the PURL data in this IA collection:
https://archive.org/details/purl_collection
Each namespace is an item, that has a JSON file with the mappings in it. So DublinCore is:
https://archive.org/details/purl_dc
and it has JSON file:
https://ia601205.us.archive.org/29/items/purl_dc/purl_dc_purl.json
Kinda cool :-)