Not sure I’m getting the issue here (what does “join table” mean in the scope of JSON/XML?), but… doesn’t how you lay out your data in JSON/XML file have zero impact in your application’s queries? You won’t be querying the JSON - you’ll be loading data from it into memory and query the memory.

I last used it a good while ago (like, 10yrs?), so you’ll have to verify how what I am about to say applies to current versions (it probably does).

Jasper is an old-school, enterprisey tool similar to Crystal Reports that attempts to give you a WYSIWYG editor for building your reports.

All in all, I’d say that it might be good if you have a reporting department full of people that only do reports and you don’t want to train as programmers. If the ones doing the reports are gonna be actual programmers, they’ll be much better off generating html/latex/whatever and converting that to pdf.