The website http://graphml.graphdrawing.org/ lists the file formats GXL, GML, XGMML or SVG. All of them, including graphML are considered to be "standards". Unfortunately there is not really a huge amount of information listed on how they play together. Some links are even dead, most of the information was written down more than a decade ago.
I created some minimalist examples to see how the file formats work and I'd tend to think there should be a way to convert them. But until this point I haven't figured out any library or python-module which can do that. (networkx seems to do a good job, but is not perfect).
There's pygraphml but it doesn't look very official.
Has anyone who provided another new standard published some kind of converter?
Also I wonder how much they are even discussed. SO only has tags for GraphML, GML (Graph Modelling Language) and SVG (which is not only limited to graphs).