1. A computer-implemented method of processing event to detect the occurrence of unusual events, said method comprising the steps of: receiving a historical event data set; classifying all events in said historical event data set according to a context in which they occurred; performing pattern analysis on said historical event data set with context classifications to generate frequent event patterns; comparing said frequent event patterns to a current event data set and to their context classification to identify unexpected event occurrences or unexpected event absences in said current event data set; and outputting an unusual event indication whenever an unexpected event occurrence or unexpected event absence is identified.