Subscription Matching Algorithm for Smart-M3

One of the properties of Smart‐M3 is to support event‐based behavior in smart spaces. The mechanism for this is the subscription/notification mechanism. The problem with the mechanism is the performance. Basically, the system should behave as if each subscription is re‐evaluated after each change to the contents of the SIB. However, this kind of naïve implementation is not scalable. The performance of SIB will decrease when the number of subscriptions increases.

A significantly more efficient subscription‐matching algorithm based on Rete network has been implemented in Aalto/CSE. The subscriptions are expressed as SPARQL queries, which are automatically translated into an incremental matcher network. Whenever new information enters the system, it is propagated through the network as far as it matches the queries. When the final piece of information arrives that satisfies a query, a notification is produced. With the test data the network provides almost constant notifications times, thus providing a tentative solution for the scalability problem. More detailed simulations and performance measurements are in progress.

The results are described in the deliverable (confidential for DIEM consortium members), which will be also presented as an article in the SAC2012 conference.