> Side effects can even be introduced - on purpose - by way of UDFs that talk to the outside world. > I've seen more than one system where the database itself

> Side effects can even be introduced - on purpose - by way of UDFs that talk to the outside world. > I've seen more than one system where the database itself was directly responsible for things like rendering final HTML for use by the end clients. I built BI Web pages entirely in PL/SQL (using some Oracle modules I can't quite recall the nams of) over twenty years ago. Got a bit hairy to keep the meta-recursive stuff in your head when hard-coding JavaScript into it, calling the next such page for each value on the page, for drill-down to the next level... Not fun, but quite doable. And with a bit more modern tooling -- as I said, this was turn-of-the-century tech -- I have no doubt it could be done much more effectively and efficiently nowadays.