A hybrid pull-push system for near real-time notifications on sensor web

World-wide sensor web generates tremendous amount of sensor data stream allowing people to observe events that were previously unobservable. Sensor web has been wildly applied in many monitoring systems; some of them are extremely time-sensitive, e.g., disaster management systems. However, with the growing amount of sensor data, the traditional request/response communication model becomes inefficient as it is based on point-to-point pulling interactions between users and data providers. In order to address this issue, publish/subscribe communication model has been proposed and applied in many applications, e.g., web blogging. The publish/subscribe model utilizes an intermediary broker on matching predefined queries with the data pushed to the broker. However, we argue that the publish/subscribe model is hard to be directly applied to sensor web due to the fact that most sensor web services are based on pulling interaction model only. For instance, more and more sensor data providers are publishing their sensor data with the Open Geospatial Consortium (OGC) Sensor Observation Service (SOS) standards, and the OGC SOS services are based on the request/response model. Therefore, in order to address this issue, we propose a hybrid pull-push system to retrieve sensor web data in a timely manner. The preliminary experimental results indicate that the proposed system is able to fetch near real time sensor streams from pull-based sensor web services.