The paper describes principles, architecture and design of a general solution for business process management systems integration with complex event processing (CEP) engines. As CEP query standards are still in early development we define a general abstract CEP Query Model and corresponding distributed infrastructure: CEP Network to abstract from specific CEP engines. We propose integration between BPEL Engines and CEP Network using intermediary bidirectional CEP Service. Key part of the solution is to represent CEP Network queries as WSRF resources. Events from CEP Network are received using WS-Notification. This approach allows using standard BPEL and does not require any changes or extensions in BPEL Engine and designing tool. We compare the proposed approach with some existing alternatives. We present a prototype which implements key components of the proposed solution and provides integration between an open source CEP Engine Esper and BPEL Apache ODE engine.