Advice on creating XML documents from MySQL

I'm posting this here because this is more PC than i-related. It just
happens that the data currently exists on an iSeries system.

This will be essential an ETL tool...

What I want to build is a MySQL database on the PC that has normalized
tables that generically define data, for example a sales order header table,
an order detail table, header notes, detail notes, a table with order-level
address information, and so on.

An RPG program may be necessary to prepare the data for download to the PC,
then a file transfer of some sort or SQL will be used to extract the data
from the iSeries into the corresponding MySQL tables. I will then need to
generate an XML document from the MySQL tables that is in a certain format
that will be imported into a vendor's software package into their database -
I expect that the vendor has either a Schema or a DTD that describes the
XML.

Here's my real issue:

I know how to extract the data from the i and I know how to create the MySQL
tables...what I need is advice on what language/tool to use to generate the
appropriate XML from the MySQL tables, based on the vendor's DTD or Schema.

TIA,
Steve