Efficient message delivery models for XML-based publish/subscribe systems

XML-based publish/subscribe (pub/sub) systems have been receiving a great deal of attention from the academic community and the industry. This research focuses on efficient pub/sub systems and considers the devising of XML-based pub/sub systems from the perspective of subscription/query and publication message delivery. Existing research mainly focuses on the efficiency of XML publication message filtering algorithms. Not much research, however, has considered using the system or the communication model in the context of XML publication messages delivery. This paper presents innovative XML delivery techniques, the cross-layer model and the peer model; both techniques make use of publisher and customer edge brokers for efficient XML subscription aggregation and publication message delivery. The primary contribution of the proposed models is the reduction of the number of XML publication message filtering and XPath query aggregation operations performed in the conventional filter-based XML multicast model, which has a high computational overhead. The main idea is to store user subscriptions at customer and publisher edge brokers which are either directly connected or close to the subscribers and the publisher, respectively. We have performed a number of experiments within a controlled local area network (LAN) environment for demonstration of the basic concepts underlying the techniques and in the Amazon cloud environment that emulates the wide area network (WAN). Both the cross-layer and the peer models can reduce the end-to-end (E2E) delay in message delivery. For example, the results obtained from experiments in a LAN demonstrate several-fold performance improvement in E2E delay for both the cross-layer and the peer models compared to the conventional filter-based XML multicast model, and the results using the cloud show an improvement as high as 64% in E2E delay for the peer model over the multicast model.