Service Composition for Efficiency and Policy Compliance

Professor Boleslaw K. Szymanski
(Rensselaer Polytechnic Institute, USA)

Sensor applications are typically composed of a number of functional components that distributed over the nodes of a sensor network, communicating and interacting with each another. Service composition is emerging as a viable approach towards the automatic synthesis of such sensor applications. However, for service composition to be practical, it has to be (i) efficient, (ii) dynamic and (iii) able to comply with policies that define security and management constraints on the use of these service components and the interconnections amongst them.

To address the first requirement, we first propose a graph-based model of sensor services that maps to the operational model of sensor networks and is amenable to analysis. Based on this model, we formulate the process of sensor service composition as a cost-optimization problem, which is NP-complete. We then propose two heuristic methods for its solution, the top-down and the bottom-up, and discuss their centralized and distributed implementations. Using simulations, we evaluate their performance.

To cope with the second requirement, we propose to use real options theory for selecting component services. Real options enhance managerial flexibility but also incur certain costs. We apply the switch options subset of the real options methodology to manage the risks of high cost that may result from the low reliability of sensors and sensor networks. Furthermore, we compare our approach with several service selection methods and show the advantage of the option-based methodology.

To satisfy the third requirement, we propose a policy model and evaluation approach to enable the users to define and check attribute-based policies, for controlling the sensor service composition process. Attribute-based policies are generic and allow us to express a wider spectrum of constraints than currently possible. Using this model and based on a previously-proposed sensor service composition algorithm, we introduce a policy evaluation method that allows for efficient checking of policy constraints. We further present a novel implementation of the proposed approach in the IBM Sensor Fabric, a middleware framework that simplifies the development of distributed, sensor network services. We also present preliminary performance evaluation results using our prototype.