15. The non-transitory computer-readable storage medium of claim 12 , wherein determining a respective hypothetical context can involve: determining a distribution over weather conditions for the distribution over location and the distribution over time; determining a distribution over context-related preferences; and/or determining a distribution over conditions related to the hypothetical context that may be inferred from publicly-available data about the distribution over other contextual variables.
19. The non-transitory computer-readable storage medium of claim 15 , wherein determining the hypothetical context involves: retrieving from a calendar a context whose associated time period substantially matches the time distribution of the hypothetical context; and setting other variables of the hypothetical context to the variables of the context retrieved from the calendar.