Adaptive Web Services for Modular and Reusable Software Development

Abstract

The provision of individual, but also composed services is central in cloud service provisioning. We describe a framework for the coordination of cloud services, based on a tuple-space architecture which uses an ontology to describe the services. Current techniques for service collaboration offer limited scope for flexibility. They are based on statically describing and compositing services. With the open nature of the web and cloud services, the need for a more flexible, dynamic approach to service coordination becomes evident. In order to support open communities of service providers, there should be the option for these providers to offer and withdraw their services to/from the community. For this to be realised, there needs to be a degree of self-organisation. Our techniques for coordination and service matching aim to achieve this through matching goal-oriented service requests with providers that advertise their offerings dynamically. Scalability of the solution is a particular concern that will be evaluated in detail.

Towards Dynamic Updates in Service Composition

“…We are currently working on applying the theory of updatable choreographies/orchestrations in the context of session types for typing a concrete language with session spawning, where choreographies play the role of global types attached to sessions and we use orchestrations for checking, via typing rules, that the code actually conforms with the specified global types. In this context, extending our contract refinement theory [5,7,9,10,12] to updatable choreographies/orchestrations would make it possible to define a notion of semantic subtyping.…”

“…We, thus, define contract refinement as the coarsest preorder over behavioural contracts which preserves correct composition when applied to members of a set of behavioural contracts (one for each role of a choreography). See [5,6,7,8,9,10,11,12] for formal definitions considering several form of communications/notions of correct composition.…”

Choreographies and Behavioural Contracts on the Way to Dynamic Updates

“…We will therefore take terms C belonging to a generic set P con being any set of terms (generated by the syntax of a process algebra) that give rise to all possible behavioral contracts as their semantics (in the form of finite connected LTSes as in Definition 3.2). For instance P con can be basic CCS (with recursion) over L prefixes and extended with successful termination 1, see [13,2].…”

“…To this aim a foundational study about coarsest refinement preorders between behavioural contracts made it possible to decide whether a service discovered on the internet can be used to play the role of a service with a given desired contract in the context of a multi-party coordination (independently of the service discovered for the other roles) [2,12,11,10,7,6], or to play a certain role in a given choreography [13,9,8], without incurring in deadlocks (and furthermore guaranteeing termination under fairness assumption). More precisely, theories of behavioural contracts have been introduced which enable reasoning about correct service composition (contract compliance) and service substitutability (contract refinement preorder) under different assumptions concerning service communication: synchronous address [13,2,8] or name based [11,10,6] communication (invocations are directed to a certain role or just based on channel names as in CCS) with patient non-preemptable or impatient invocations (waiting admitted when invoking services, as in CCS communication, or not admitted, as for the ready-send primitive of the Message Passing Interface) [12,7], or asynchronous communication with queues [13,9].…”

“…We also deal with the problem of directly relating discovered behavioral contracts with choreographies. Such a theory is presented for the case of synchronous address based communication (where invocations are directed to a certain role) with patient non-preemptable invocations [13,2]. The results for other forms of communications are just summarized here.…”