Writing a custom app and do you want to query our sensors? JSON can help you. The built-in webserver HTML uses JSON to query the sensors via REST API.
2 JSON API calls you need to know:
http://IP_ADDRESS/probe_list.json
this call returns the list of sensor probes connected to the Sensorgateway and their settings
http://IP_ADDRESS/probe_update.json
this call returns the latest values of all the sensor probes.