A Two-Phase Approach to Subscription Subsumption Checking for Content-Based Publish/Subscribe Systems

The efficiency of subscription subsumption checking remains a key issue for content-based publish/subscribe systems. In this paper, we propose an efficient data structure called subscription subsumption graph (SSG). This data structure could differentiate the two types of subsumption relationships and help speed up the process of subsumption checking and subscription cancellation. We then present a two-phase approach to subscription subsumption checking. Phase one is mainly about checking of non-numeric constraints by using an index structure which could help filter out most of irrelevant subscriptions while phase two is about checking of remaining numeric constraints where SSG is employed. Finally, we introduce an efficient SSG-based unsubscription algorithm that could find out which subscriptions need to be forwarded without any redundant computing. We illustrate the advantages of this approach by carrying out extensive experiments.