SQLite is a relatively full featured RDBMS, albeit using a single db file instead of a client server model. It's a bit more than 'fopen with a different name'. Just about anything you might want to do with MySQL can be done with SQLite. I wouldn't build an authentication system with it, but it's good for basic data storage / logging / etc.

I've been working with JSON a bit lately, although it's primarily in XHR requests, you might consider it an alternative to XML.

Prepare some tests with XML / SQLite / JSON and run benchmarks against them. I'm guessing JSON will be on top with SQLite not far behind and XML the slowest / most intensive of the bunch.

__________________

I reject your reality, and substitute my own.