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.
18. The computer-readable storage medium of claim 13 , wherein the computer-readable storage medium stores additional instructions that, when executed, cause the computer to perform additional steps comprising: receiving bulk upload of event data through an event posting interface; and modifying the context graph based on the received bulk upload event data.