1. A method of discovering one or more partially periodic patterns in event data, the method comprising the steps of: transforming at least a portion of the event data into event classes such that the event data is non-application-dependent; determining period lengths for each event class in accordance with occurrences of events in the transformed event data, wherein determination of the period lengths for each event class takes into account a predetermined time tolerance value; and merging event classes into one or more temporally associated groups in accordance with the period lengths to form the one or more partially periodic patterns.