1. A computer-implemented method comprising: receiving, by a stream computing system, data representing the values of one or more data attributes of an event in a stream of events; obtaining a hierarchical analytic model that defines, for a plurality of classes, one or more data attributes of the event to be evaluated by one or more respective attribute-specific and class-specific criteria in a predetermined order; evaluating the values of each of the one or more data attributes according to the respective attribute-specific and class-specific criteria in the predetermined order determining that a first value of a first data attribute satisfies one or more particular criteria for a first class; and assigning the first class of the plurality of classes to the event.