Recap, and where to go next

Pure Datalog terminates, is decidable, and is polynomial in the data: recursion you can trust. Add negation and arithmetic and questions like containment and emptiness turn undecidable.
Non-recursive Datalog is exactly relational algebra, recursion adds a least fixed point, and that is just WITH RECURSIVE in SQL.
Step outside the pure fragment with arithmetic and strings, and bring in JSON with the value type, at the cost of the termination guarantee.
The same ideas run real systems: Soufflé, CodeQL, and Datomic.

Keep going: the language spec, the in-browser playground, and the case studies (theorem proving, program analysis, and more) continue from where these slides end.