1. A method for determining similarity between a first event set, the first event set comprising a first plurality of event types, and a second event set, the second event set comprising a second plurality of event types, the method comprising the steps of: randomly mapping the first event set to a multidimensional vector-Q; randomly mapping the second event set to a multidimensional query vector-q; and determining similarity of the multidimensional vector-Q with the multidimensional query vector-q according to: &par;Q−q&par;&lE;SV, where SV&equals;a predetermined similarity value.