Taken directly from XGMML website

XGMML (eXtensible Graph Markup and Modeling Language) is an XML application based on GML which is used for graph description. XGMML uses tags to describe nodes and edges of a graph. The purpose of XGMML is to make possible the exchange of graphs between differents authoring and browsing tools for graphs. The conversion of graphs written in GML to XGMML is trivial. Using XSL with XGMML allows the translation of graphs to different formats. 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, as any other XML application, can be mixed with other markup languages to describe additional graph, node and/or edge information.

<graph directed="1" id="42" label="Hello, I am a graph">
<node id="1" label="node 1"> </node>
<node id="2" label="node 2"> </node>
<node id="3" label="node 3"> </node>
<edge source="1" target="2" label="Edge from node 1 to node 2"> </edge>
<edge source="2" target="3" label="Edge from node 2 to node 3"> </edge>
<edge source="3" target="1" label="Edge from node 3 to node 1"> </edge>