A Constraint Satisfaction Approach to Non-functional Requirements in Adaptive Web Services

While agility is a key driver for business processes as envisaged in Service Oriented Architecture (SOA) deployments, very little thought has been put forward in the direction of managing the non-functional requirements adaptively. Adaptive SOA and Web services require mechanisms for enabling dynamic adaptation in SOA systems with a requirement of keeping service interfaces intact, while manifesting dynamism in the behavior of a service, at the same time maintaining consistency with the concomitant policies. Policy reconciliation between service providers and service requestors in such adaptive SOA systems is often a difficult requirement to satisfy owing to the generality of the policies not only those associated with a single service provider but across multiple services. Addressing this dynamic adaptation requirement for policy based non-functional requirements, we present a constraint satisfaction based framework to represent, model, and work with policy based non-functional requirements in Adaptive Web services. We illustrate this with concrete example industrial use cases to drive home the benefits of constraints based approach. We also conjecture that the extensions of the approach in form of constraint hierarchies and soft constraints can encompass two fundamental requirements in adaptive SOA and Web services-- policies requiring differential QoS, and policies requiring optimal provider selection.