DOCBOOK: newbie: partitioning docbook documents

Hi,

could someone point me to a tutorial or the part in the documentation that 
explains how to partition a document into many files? At the moment I would 
like to do two things:

- put each section of an article into a separate file
- and put code examples that I use as programlistings in a separate file

do I have to declare external entities for that? I have played around with 
that but ran into problems (CDATA section was not parsed when in a separate 
file). could anyone give me a working example for the two things I describe 
above.

thanks in advance,

robert