generative building of xml?

I am generating, processing and eventually serializing
several XML streams.   I was wondering if this was possible 
to do with lxml?

Here's the setup.  I've got several databases
generating XML content (which can be quite large), I really want
to be able to process the database record progressively 
generating XML and sending out on its own stream. 

An aggregator/filter  (elsewhere) will read the streams 
and parse them processing similar members and generate 
a new stream based on the combined streams.

DB1    DB2   DB3   Core database
XML    XML   XML   XML genaration
 WS     WS   WS     delivery over a stream using generator 
 |      |     |
 +------+-----+
       AGG          Parse and match incoming streams (iterparse)
       XML
       WS           send resulting merge as XML using generator.

So the questions:

1.. Does anybody have a recipe to build a recursive generator using
    Element?

2.  Given the above generator, is there any such 
    thing as a generator version etree.tostring?

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-- 
Kristian Kvilekval
kris <at> cs.ucsb.edu  http://www.cs.ucsb.edu/~kris w:805-636-1599 h:504-9756