The web service is available at http://atom.research.microsoft.com/sensordatahub/service.asmx
If you click on a specific method, it shows you the arguments that you need to pass in. In MSRSense Tutorial (https://research.microsoft.com/research/nec/msrsense/tutorial-v0.2a.pdf), there is a section about using the DataHub API. In that document, you can find the format for SensorInfo (SDML), which is an argument for the register sensor call.
Jie