1. A computer-executable method performed by a server to provide user information to a recommender, comprising: receiving, from the recommender, a registration for notification of changes to a context graph, wherein the context graph includes information about user behavior and/or user interests; receiving, from a mobile device, event data derived from contextual data collected using detectors that detect the mobile device's physical surroundings; modifying the context graph based on the event data; determining that the modification to the context graph matches the registration; and sending a notification of context graph change to the recommender.