Unidata has created a new version of ncdump, ncxdump, which dumps XML. They are working on ncxgen which will read the XML. They also made a DTD.
I downloaded their stuff for us to examine.
netcdf DTDOverall, the netcdf DTD is very simple, much simpler the what we are trying to do. This is not surprising, since they don't have to deal with grouping or other structure issues, and they have far fewer data types.
example XML file
As to representing the data, the netcdf DTD has it as '#CDATA', and the example XML shows a variety of formats for the data.
One thing that I noticed in the netcdf example XML is that they deal with missing/uninitilized values. We haven't discussed this yet.