Large XML manipulation within PHP

I work for a company that has chosen to use XML (Software AG Tamino XML
database) as its storage system for an enterprise application. We need to
make a system wide change to information within the database that isn't
feasible to do through our application's user interface. My solution was to
unload the XML collection in question, open it, manipulate it, then write it
back out. Problem is it's a 230+MB file and even with PHP's max mem set to
4096MB (of 8GB available to the system) SimpleXML claims to still run out of
memory. Can anyone recommend a better way for handling a large amount of XML
data? Thanks.

-- 
--Steve Gula

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