This is a fantastic resource. The author only briefly covers library databases, but there's so much more in structured querying that could be worth covering.

For example, you can use Sparql to perform structured queries on Wikidata (a structured database version of Wikipedia) to get well beyond unstructured documents.

Here's every person in Wikibase that was born in NYC: https://query.wikidata.org/#%23Humans%20born%20in%20New%20Yo...