1. An event processing system, comprising: an event bus configured to receive a stream of events, each said event having a predefined event type; an event processing agent including at least one first processor, the event processing agent being configured to execute predefined queries on the events, each said query conforming to a query language, the query language being enhanced via a semantic extension corresponding to an ontology; and an ontology management component in communication with the event processing agent, the ontology management component including: a first storage location storing mappings between concepts of the query language and concepts of the ontology that enhances the query language, and processing resources, including at least one second processor and a memory, configured to, when an enhanced query, defined in accordance with the query language enhanced via the semantic extension and to be executed on a received event by the event processing agent, includes references to ontology concepts using semantics extension enhancement in the enhanced query, generate, in accordance with the stored mapping between the concepts of the query language and the concepts of the ontology that enhances the query language, a translated query with the references to the ontology concepts in the enhanced query being translated into queries processable by the event processing agent in accordance with the query language without the semantic extension enhancement; wherein the concepts of the ontology are classes, and wherein the generating of the translated query comprises, for the enhanced query: retrieving a class definition for all referenced classes from a corresponding ontology; determining whether the referenced classes are marked as being handled; when the referenced classes are marked as being handled, transforming the respective class definition to the query language, and compiling the translated query; and when the referenced classes are not marked as being handled: when the respective class does not have a corresponding mapping, replacing the class with a union of all of its sub-classes, when the respective class has a corresponding mapping but no sub-classes, removing the reference to the class, and when the respective class has a corresponding mapping and any sub-classes, adding a union with all sub-classes to the class and marking the class as handled.