Rule-based systems and languages are successful in many application areas such as business rules or active database systems. The goal of the Demaq project is to investigate the feasibility and benefits of using a declarative, rule-based programming language to simplify the development of complex, distributed applications. For this purpose, we propose a novel programming paradigm based on messaging, queues and declarative rules. We focus on evaluating whether the proposed, rule-based approach can be used to implement complex application patterns. We use Enterprise Application Integration (EAI) as an example application domain, as EAI applications involve multiple, heterogeneous systems with complex interaction patterns. We discuss whether and how these application patterns can be implemented using our rule language