1. A method in a computing device for retroactively analyzing a log of context attribute values associated with a user of the computing device, each context attribute value contained by the log being stored with an indication of a corresponding data item and an indexing value, the computing device comprising a characterization module and at least one application, the method comprising: employing a processor executing computer-executable instructions stored on a computer-readable storage medium to implement the following acts: operate the characterization module to: receive a specification for analyzing values among the stored values, the specification specifying one or more context attributes, a range of indexing values, and an analysis technique; retrieve stored values for the specified context attributes associated with the user of the computing device within the specified range of indexing values, wherein a first subset of the stored values for one of the specified context attributes is associated with a first source device, and a second subset for the stored values for the one of the specified context attributes is associated with a second source device; and apply the specified analysis technique to the retrieved values to produce an analysis of the context attributes that infers information representing at least one of the user's physical activity, emotional state, or cognitive load; and operate the at least one application to receive and use the inferred information.