[zaarn]

>A DB schema cannot fully validate stored data against the logic.

Postgres actually lets you run triggers and similar that can validate data arbitrarily. You can even do web requests with the right extension.

If that is not enough, you can run Python code in your database instead and do the same thing with a slightly more powerful language for general purpose computation.

You could write the entire logic of any business app in a PG database and only use the app as a shiny view layer.