XPath: Looking Forward

by Dan Olteanu, Holger Meuss, Tim Furche, François Bry
Institut für Informatik, Ludwig-Maximilians-Universität München,Germany

The location path language XPath is of particular importance for XML applications since it is a core
component of many XML processing standards such as XSLT or XQuery.  In this paper, based on axis
symmetry of XPath, equivalences of XPath 1.0 location paths involving ``reverse axes'', such as ancestor
and preceding, are established.  These equivalences are used as rewriting rules in an algorithm for
transforming location paths with reverse axes into equivalent reverse-axis-free ones.  Location paths
without reverse axes as generated by the presented rewriting algorithm enable efficient SAX-like
streamed data processing of XPath.