For my web site I parse numerous XML files with PHP and use that data to populate databases, as well as generate web pages from the data. There is a free and open source library that I use to power this functionality, called nusoap. The library is very powerful and includes tools to parse a variety of types of web services. The drawback is that the documentation is non-existant. However, you may be able to find instructions for simply parsing an XML file through the library. The system works by converting the data in the feed into an array that can then be used by your PHP script to display or process the data.

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