DOCBOOK-APPS: Format conversion between PDF and DocBook

[Ho <ho@dpi.inpe.br>]

I have been searching around but so far
I had no direct answers. Probably I did not find the right place.

Basically I would like to make a
"Format conversion between PDF and DocBook"

My intention is to write Servlets that make the calls to API
and outputs either PDF or DocBook depending on the request.

The best I could get was from Sun's site at
http://www.sun.com/software/xml/developers/fop/

In one step processing (without FO) it would be:
java org.apache.fop.apps.XalanCommandLine
                presentation.xml slideToFO.xsl presentation.pdf

In that case I need the  slideToFO.xsl,
where to get a DocBookToFo.xsl ?

I have no hint about the conversion in the opposite direction,
that is, from PDF to DocBook.

So, in a two step approach, where do I get a DocBook-FO converter?
In any case (1 or 2 steps) I would need a  FoToDocBook.xsl.

I might be wrong. Jade or OpenJade cannot be called as a Java API.

Any kind help is much appreciated.
Thank you
Carlos