The document discusses using a rule-based service bus to control data flows in patient-centric hospital information systems. It proposes a service-oriented architecture with loose coupling between components and data flow controlled by a rule engine. Specialized systems can be integrated through a plug-in mechanism and communicate via messages distributed by the rule engine, allowing for seamless integration and workflow across application borders. The approach was prototyped with open source components integrating a PACS and ERP system.