1. Mobile middleware, comprising: a Context Monitoring Query (CMQ) processor for storing requested CMQS, receiving sensor data from sensors, monitoring whether the stored CMQs are satisfied, and transmitting an event according to results of the monitoring; and a Reduced Source Cover (RSC) manager for controlling activation of the sensors so that, of the received sensor data, only data about context elements belonging to a minimum context element set (RSC) required to determine whether the CMQs are satisfied is generated.