John Punin has released a draft of Extensible Graph Modelling and Markup Language (XGMML), along with examples and software.

XGMML is based on Graph Modeling Language, but uses XML to express the information rather than the text format used by GML. Because XGMML is an XML application, it cn take advantage of XML tools, notably XSLT.

While XGMML is useful for general graphing functionality - "to make possible the exchange of graphs between differents authoring and browsing tools for graphs." - it can be used for Web site mapping as well:

"XGMML was created to be used for the WWWPAL System that visualizes web sites as a graph. Web Robots can navigate through a web site and save the graph information as an XGMML file."

XGMML can also be used to represent RDF information or other structures like PowerPoint documents.