annotation application for docbook

Hello,
we're currently developing an annotation system for the Web.
Guess what: we've based it on the DocBook DTD.

My question would be what the community expects:
A system which,
1. once a book is in it's final stage, lets user annotate some specific 
elements,
2. lets users annotate a document all the time, even during its creation.

The problem for #2 would be that I need to reference each paragraph in a 
1to1 relationship with my annotations, e.g. paragraphs and chapters can 
be added without anything getting out of sync. Obviously, this would 
make it much more complicated than #1, which would loose all annotations 
once there's a new version of the book released.
As far as #1 is concerned, the solution would probably be to add anchors 
to the finished book after specific items, like </para> etc., and 
referencing those anchors using the chunk name with an incrementing id 
for the para-tags. However this would be much less flexible!
For #2 I could create a preprocessor populating all the tags I want with 
"id" parameters, converting it to a new XML document, the user should 
use from that moment (hence establishing the 1-1 relationship). However, 
the possibility arises that the user creates id tags by himself, or 
wants to modify some afterwards. Could I simply not allow this? ;-) 
Furthermore, I'm not allowed to create new parameters on the fly, since 
modifying the DTD is not allowed in this case, is it? (I could create my 
own idx parameter or whatever...)

I hope you could follow and I would be thankful for any remarks on this 
subject.

Best regards,

-- 
Jean-Marc Roth