13. A computing system comprising: one or more processors, a non-transitory computer-readable medium coupled to the one or more processors having instructions stored thereon that, when executed by the one or more processors, cause the one or more processors to perform operations comprising: receiving, from a mobile device, event data derived from contextual data collected using detectors that detect a physical context surrounding the mobile device; modifying a context graph that stores facts and assertions about a user's behavior and interests using the event data; in response to determining that there exists a registration for notification of changes that matches the modification to the context graph, sending a notification of context graph change to a recommender.
13. A computing system comprising: one or more processors, a non-transitory computer-readable medium coupled to the one or more processors having instructions stored thereon that, when executed by the one or more processors, cause the one or more processors to perform operations comprising: receiving, from a mobile device, event data derived from contextual data collected using detectors that detect a physical context surrounding the mobile device; modifying a context graph that stores facts and assertions about a user's behavior and interests using the event data; in response to determining that there exists a registration for notification of changes that matches the modification to the context graph, sending a notification of context graph change to a recommender. 15. The computer-readable storage medium of claim 13 , wherein the event data includes high-level event data generated by the mobile device from contextual data.