GHNS Specification
The main specification is a docbook-maintained normative document. It comes with DTDs for the data files and the providers files. These files are also available in XSD format for the data files and the providers files. For reference, have a look at the data file example and the providers file example.
DXS Specification
The webservice is being standardised by its WSDL file, as well as the additional WSGUI file for visual representation.