We have been working on a shout board ( simple non-threaded posting forum) at www.nebulawebdesigns.com. The cool thing is the XML database and PHP that drives it all. If you get a chance, have a look let me know what you think. Or if you have any ideas or gotchas you have encountered with XML data storage and PHP. - Thanks

XML in PHP can be a bit of a strain unless you have XSLT support enabled.

XSLT makes life SOOO much easier IMHO.

I embarked on the XML adventure because the hosting site did not have database access and I had been looking for an excuse to really learn what XML was meant to do. It seems to be an excellent data storage format. Any though I am not using any standard DTD, I am strictly staying with well formatted XML ( as described on www.w3schools.com ).

I found PHP's xml_parser_create, xml_set_element_handler, and xml_parse_into_struct to be emensely useful. But I do have concerns about performance as my XML (flat file DB) grows. The whole file is read into an array, and it seems rather beastly on system resources. I am not sure how XSLT can help me.

Just make an XSL stylesheet and feed it and the XML file to Sablotron, PHP's built-in XSLT parser.
You won't even have to parse the XML manually, sans any filtering/modifications you want made before Sablotron kicks in.

Sablotron isn't built into PHP you have to install it manually and then recompile PHP. It's only an RPM so it isn't too difficult. However you'll probably need an up to date version of the javascript libraries and expat to install sablotron.

I think it will be built in as XSL becomes more common as it's so powerful for use with XML.