I think there are a couple of issues here mixed up that you need to find / think about. Is it that your input data is XML, or are you looking for a DBMS that *stores* as XML? If the former (and I hope so), then you'll probably want to check out all the XML modules for importing it.

To manipulate *any* 'database', from Oracle down to CSV text-files, use DBI - it means you can use the same code to address your data even if your database needs change. If you don't want to run some kind of server on your machine, check out DBD::CSV etc.

If you *are* looking for an XML-based DBMS, well I hear there are a few about, but it's not the most *efficient* way to manipulate bytes - you'd probably be better offconverting back and forth using the aforementioned XML modules.

Hope this helps
Ben