Section: Application Domains

Web Services

Participants : Stefan Haar, Serge Haddad.

Specific applications targeted by MExICo include the problem of adaptation in Service-Oriented Computing (SOC). The challenge is here twofold, stemming both from the distributed nature of services (scattered over the entire web) and their heterogeneous origins.

Context

Web services have become the most frequently used model of design and programming based on components for business applications. Web service languages like BPEL have useful constructors that manage for instance exceptions, (timed guarded) waiting of messages, parallel execution of processes, distant service invocations, etc. Interoperability of components is based on interaction protocols associated with them and often published on public or private registers. In the framework of Web services, these protocols are called abstract processes by contrast with business processes (i.e. services). Composition of components must be analyzed for several reasons and at least to avoid deadlocks during execution. This has led to numerous works that focus on compositional verification, substitution of a component by another one, synthesis of adaptators, etc., and triggered a push towards a unifying theoretical framework (see e.g. [115] , [119] )

Problems

Interoperability requires that when a user or a program wants to interact with the component, the knowledge of the interaction protocol is enough. Our previous works have shown that the interaction protocols can be inherently ambiguous: no client can conduct a correct interaction with the component in every scenario. This problem is even more complex when the protocol can evolve during execution due to adaptation requirements. The composition of components also raises interesting problems. When composing optimal components (w.r.t. the number of states for instance) the global component can be non optimal. So one aims at reducing a posteriori or better on the fly the global component. At last, the dynamical insertion of a component in a business process requires to check whether this insertion is behaviorally consistent [121] , [109]

We do not intend to check global properties based on a modular verification technique. Rather, given an interaction protocol per component and a global property to ensure, we want to synthesize an adaptator per component such that this property is fulfilled or to detect that there cannot exist such adaptators [106] . In another research direction, one can introduce the concept of utility of a service and then optimize a system i.e. keeping the same utility value while reducing the resources (states, transitions, clocks, etc.).