1. An apparatus comprising: a memory for providing a context-aware service; a context-aware service object (CAS) management module which manages CAS information of a CAS and a context which is defined by the CAS; a sensor management module which manages sensor information of a sensor and requests the sensor to observe knowledge; and a context management module which is provided changed knowledge from the sensor when there is a change in the knowledge, determines whether the provided knowledge satisfies a context provided by the CAS management module, and informs the CAS management module of a CAS which defines a context which is provided by the CAS management module when the knowledge satisfies the context, wherein the CAS management module requests the CAS to provide a service if the CAS management module is informed of the CAS by the context management module, wherein when a new sensor is added, the sensor management module registers sensor information of the new sensor and when a new CAS is added, the CAS management module registers CAS information of the new CAS and a context defined by the new CAS, and wherein the sensor information is allowed to be deleted in response to a removal request from the sensor, and the CAS information and the context are allowed to be deleted in response to a removal request from the CAS, and wherein the CAS is a server object while the sensor is a client object, the context being determined based on knowledge provided by a plurality of sensors and information on an operating environment.