Integrating complex systems like application systems or whole enterprises by means of exchanging electronic business data requires not only the passing of the business data itself in form of business events between the systems but also ensuring that the relevant business events are passed at the right time as well as in the right order. This is called the integration problem: the formal definition and execution of the exchange sequence of business events between complex systems. Many insufficient standard proposals are currently being brought forward to address the integration problem. This contribution revisits the requirements of complex systems integration and proposes superior alternatives in approaching and solving the integration problem.