Abstract: An apparatus, method and computer program for evaluating an event in a data processing system, wherein the event comprises a plurality of predicates, the apparatus comprising: a receive component operable for receiving the event; an analyze component, operable for analyzing a plurality of first relationships between the plurality of predicates and a plurality of first values; an order component, operable for ordering the plurality of predicates; an evaluate component, responsive to the order component identifying that one of the plurality of predicates is a primary predicate, operable for evaluating the event for the primary predicate and for determining a result, wherein the result indicates whether the event is true or false for the primary predicate; and an update component, responsive to the evaluate component evaluating the event for the primary predicate, operable for updating the plurality of first values.