Our research is motivated by the scaleability, availability, and extensibility challenges in deploying open systems based, enterprise operational applications. We present Delta's mid-tier Operational Information Systems (OIS) as an approach for leveraging its legacy operational OLTP infrastructure, to participate in the emerging world of electronic commerce, as well as enable new applications. The approach is to place minimally intrusive 'taps'into the legacy OLTP systems to capture transactions as they occur for consistent replay in the mid-tier OIS. One important issue addressed by our work is the processing, and dissemination of information in the mid-tier system itself, potentially serving hundreds of thousands of access and display points, distributed across a highly geographically distributed system (e.g. airports world wide), and also involving large `working sets' of operational data, used by applications that require rapid response and also rapid recovery ...