The XML_XPath PEAR Class allows easy manipulation, maneuvering, and querying of a domxml tree using both xpath queries and DOM walk functions. It uses an internal pointer for all methods on which the action is performed. Results from an xpath query are returned as an XML_XPath_Result object, which contains all the DOM functions from the main object. This class tries to stay as close as possible to the DOM Recommendation. It is important to note that this is only an interface for the PHP domxml library. It depends on that library available (--with-dom) and hence requires PHP 4.2.1. This class is useful if you are looking for a fast implementation to XML documents.
The SODA Native XML Database System is a native XML database that provides efficient management of large amounts of XML data. It is based on a multi-user, client-server architecture with a generic query processing layer that can easily support different query languages. In this lightweight version, user- defined indexes and query optimizations have been removed, however full transaction support (commits and rollbacks) and crash recovery are available.
xpath2rss is an XPath to RSS scraper. XPath makes a better HTML scraper than regex (the typical solution) because it understands the structure of the document, rather than just treating it as a big string. As a result, xpath2rss is a more reliable scraper, and much easier to use, once you get the hang of XPath.