Whether to use SQL , XML/JSON?

After doing my exercise in school, I use Sqlite to store my data. But there's XML / JSON [ I haven't tried yet, but I prefer JSON becaus开发者_开发技巧e its' simplicity ], they're used to store data too. And they seems popular, there's JSON for C#,C++,py ....

I wonder when to use these ones ? And I'm happy to hear about theirs performance too, I care most about speed ;) Thanks.

XML and JSON are actually used primarily to transmit data between processes or systems.

I have seen applications that use XML as a database. If you're going to do this, you'll have to break your data down into very distinct, small units that can each be stored in a separate file.

Overall, in my opinion and experience, if performance is your primary concern, file-based data storage in XML or JSON will almost never perform remotely close to an actual SQL relational database platform unless your dataset is extremely tiny.