The Extreme Markup proceedings are starting to become available. Very interesting stuff. Here is one that discusses an approach for an extended XPath that can address directed graph needs. Note that a very practical example where this is needed is shown in the IsaViz editor, wherein a form of "CSS" is used to apply styles to a DLG . However, the IsaViz code does not use the method presented in this paper. Generalizing XPath for directed graphs IsaViz: http://www.w3.org/2001/11/IsaViz/