Creating XML document

  Hi,
I'm doing some research for possible XML project, and I need to clarify
a few things with all you experienced people out there.

1. How do I go about creating XML document/file from a database/process.
I understand I have two options, use DOM tree to build document and
write it to the file at the end, or use brute force to write markup
directly into the flat/IFS file (and then maybe, validate it through
parser, just in case). Of course, DOM method is more sophisticated and
less error prone, but my biggest concern would be size and memory
requirements. It is a big project, and XML is likely to have 1 000 000s
of  records with 10s of nodes each. So can that fit into the memory
using DOM or I'll have to write smart program to write records
sequentially and ensure some degree of tag/document validity and
well-formedness. Or is there some third way I have no idea about?

2. What would be the pros/cons for doing it in Java vs. RPG. This can
sound as a naive question, but we are very early in the project and XML
part might be made rather independent. Application is written in
RPG/COBOL/SQL, but that itself is not limiting factor. General team
skill set is on the
RPG side, but there is a will to take this opportunity and learn.
Besides, after checking a few samples of RPG using IBM's C++ parser, ...
that definitely doesn't look pretty, and I'm afraid that as project
progresses and requirements become more complex, we are going to regret
for not starting it in Java.

3. Give me some idea about general sizing. Obviously, lots of file
storage and FTP- ing will be involved. How much bigger XML file gets
compared to its DB2 counterpart? In average, assuming that we aren't
going to be over creative when it comes to tag names.

4. Should we develop DTDs , or take simpler route? Receiving side is out
of our organization (and control), so DTD might be a safe bet. What is
used for creating DTD these days? Some designing  tool ?

5. If we decide to go Java, what parser is better, IBM's or independent.

I have so menu more questions, but this should be enough to get me
started planning. Thanks so much in advance for devoting me some of your
time,

Ben.