If you want to export to Visio, export to VDX which is the Visio Document XML format. IIRC it's documented on the Microsoft site, and I even wrote a VXD exporte

If you want to export to Visio, export to VDX which is the Visio Document XML format. IIRC it's documented on the Microsoft site, and I even wrote a VXD exporter for the Graphviz open source project which I then used for Instaviz. While developing your own exporter, you can use the free Microsoft Visio Reader to examine your output to see if it conforms.