Time-triggered buffers for event-based middleware systems

Application developers utilizing event-based middleware have sought to leverage domain-specific modeling for the advantages of intuitive specification, code synthesis, and support for design evolution. For legacy and cysber-physical systems, the use of event-based middleware may mean that changes in computational platform can result anomalous system behavior, due to the presence of implicit temporal dependencies. These anomalies are a function not of the component implementation, but of the model of computation employed for supporting system composition. In order to address these behavioral anomalies, the paper presents an approach where time-based blocks are inserted into the system to account for the temporal dependencies. An advantage of capturing the system composition in a domain-specific modeling language is the ability to efficiently re factor an application to include time-triggered, event-based schedulers. This paper describes how an existing event-based component topology can be modified to permit a time-triggered model of computation, with no changes to the existing component software. Further, the time-triggered components can be deployed alongside standard publish/subscribe methodologies. This strategy is beneficial to the maintenance of existing legacy systems upon upgrade, since the current operational mode could be maintained with minimal changes to the legacy software even under changes to the target platform which alter execution speed. These time-triggered layers are discussed in three permutations: fully triggered, start triggered, and release triggered. A discussion is provided regarding the limitations of each approach, and a brief example is given. The example shows how to apply these triggering approaches without the modification of existing components, but instead through the insertion of triggered buffers between legacy components.