I. Introduction
With the spread of computers and sensors, many kinds of and a large amount of data became available for capturing what has happened in the real world. The something that has happened is called an event. Event processing [1] means computational operations on events, and we also call a set of data that represents an event in the real world an “event”. To extract useful knowledge from the huge amount of data, complex event processing (CEP) [1] has been receiving attention. Developing an efficient method of CEP is expected to innovate in event processing.