An important requirement of pervasive applications is that of data collection, aggregation and dissemination. Event communication middleware based on the publish/subscribe paradigm has been used extensively to address these data flow requirements. In addition to the data flow, the designer of a system may also want to regulate the actions performed by the components in order to implement some constraints and policies. For example, the designer may want to ensure that actions performed a set of components on receiving an event notification are triggered in a specific sequence. In this paper, we propose a framework to implement such constraints by regulating the flow of events in the middleware. Since components perform actions on receiving events, by controlling the notifications delivered to the components and the sequence in which they are delivered, the order in which actions are performed in the application can be controlled. We have implemented the framework in the context of two event services, one in C++ and another in Java. We give several examples demonstrating the use of the proposed approach.

To satisfy the stringent QoS requirements of distributed real-time embedded (DRE) systems, middleware services customized to the specific needs of the application may be needed. This problem is often attacked by reimplementing all or large portions of an existing middleware service, which can be a time-consuming and an error prone task. In this paper, we propose a model-driven approach for middleware customization. To enable this approach, we propose event communication framework (ECF), a customizable middleware framework which provides a number of different options for implementing various features of event communication. To determine when to exercise each option, we have performed experiments to identify the application contexts in which each ECF mechanism performs better than the others. Heuristics from these experiments have been incorporated into algorithms which analyze high-level specifications of application scenarios to identify where ECF customizations can be applied. We provide configuration tools that generate customized push paths for event notifications using a combination of code synthesis, weaving and transformation techniques. We have applied our approach to the application scenarios in the Boeing BoldStroke system.