Querying XML data over DHT system using XPeer

DHT systems like Chord, Pastry, CAN and Tapstry can only handle semantics-free, large-granularity requests for objects by identifier (typically a name). How to implement the content-based query in DHT system is a challenge. Query the XML data using XPath language can provide expressiveness for the DHT system. In this paper, we propose an XML-based content query system, termed as XPeer, built on DHT systems like Chord, Pastry or Tapstry. Besides the inherent properties provided by DHT, XPeer has several unique features. First, XPeer can utilize XML to implement content-based query using XPath as the query language; Second, XML data in XPeer can be totally heterogeneous, without conforming to the same XML schema or DTD. Third, XPeer can support range query over DHT. Finally, the XPeer can be easily extended to real P2P application like Napster, Gnutella and Freenet.