The Best of Both Worlds: Combining XPath with the XmlReader

Dare Obasanjo discusses the XPathReader, which provides the ability to filter and process large XML documents in an efficient manner using an XPath-aware XmlReader. With the XPathReader, one can sequentially process a large document and extract an identified sub-tree matched by an XPath expression.

http://msdn.microsoft.com/XML/default.aspx?pull=/library/en-us/dnexxml/html/xml05192004.asp