SGML to XML: Should I switch? How to switch?

[Euis Luhuanam <eluhu6@gmail.com>]

This is my first post. I have tried to browse the mail-archive, the
FAQ list, Google, with no luck. Apology, if this message should
be posted to "docbook" or worse, it has been answered several
times.

I have been using DocBook SGML for a while with Debian tools
(and  recently with Ubuntu). It works, and nothing is needed to
be fixed, except the infamous questions like: "Why not XML?"
Frankly, my answer is that I have no idea why to switch and
how to switch?!

May I know where to find detailed information about these
issues? I have got two types of issues.

First, how much do I need to convert my current headers.
A typical "main.sgml" would look like this following:
=============================
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V4.2//EN" [
        <!ENTITY % ec0 SYSTEM "c0/c0.ent">
        <!ENTITY % ec1 SYSTEM "c1/c1.ent">
        ...
        %ec0;
        %ec1;
        ...
]>
<book>
        &c0;
        &c1;
        ...
</book>

whereas "c0.ent" might look like this following:
=================================
<!ENTITY c0  SYSTEM "c0/c0.sgml">
<!ENTITY c01 SYSTEM "c0/c01.sgml">
<!ENTITY c02 SYSTEM "c0/c02.sgml">
...
=================================

Second, how would the command lines look like?
Usually in Debian/Ubuntu, it will be like this following:
==================================
% rm -f c9/c93-indeks.sgml HTML.index
% collateindex.pl -N -o c9/c93-indeks.sgml
% sgmltools -b onehtml -j "-V html-index" main.sgml
% collateindex.pl -o c9/c93-indeks.sgml HTML.index
% sgmltools -b pdf main.sgml
===================================

Thank you for any clues/URLs.

References:
* "DOCBOOK: sgml vs xml"
  http://lists.oasis-open.org/archives/docbook/200303/msg00166.html

* "DocBook and XML" http://www.docbook.org/tdg5/en/html/appb.html

* "SX" http://www.jclark.com/sp/sx.htm

-- 
EL6