The nature of data in enterprises and on the Internet is changing. Data used to be stored in a database rst and queried later. Today timely processing of new data, represented as events, is increasingly valuable. In many domains, complex event processing (CEP) systems detect patterns of events for decision making. Examples include processing of environmental sensor data, trades in nancial markets and
RSS web feeds. Unlike conventional database systems, most current CEP systems pay little attention to query optimisation. They do not rewrite queries to more e cient representations or make decisions about operator distribution, limiting their overall scalability. This paper describes the Next CEP system that was especially designed for query rewriting and distribution. Event patterns are speci ed in a high-level query language and, before being translated into event automata, are rewritten in
a more e cient form. Automata are then distributed across a cluster of machines fo detection scalability. We present algorithms for query rewriting and distributed placement. Our experiments on the Emulab test-bed show a signi cant improvement in system scalability due to rewriting and distribution.