The node descriptor file (at /osdl.js) is a JSON formatted string that describes the sensors and/or actuators provided by the node. The string contains four arrays: General, Sensors, Triggers and Actuators. The general array contains information that applies to all sensors,triggers and actuators on that node. The remaining arrays define zero or more interfaces of the sensors, triggers and actuators on that node. Control nodes do not define their own interfaces, instead interacting with the interfaces defined on other nodes.