Daniela Berardi

Automatic Composition of E-services That Export Their Behavior

The main focus of this paper is on automatic e-Service composition. We start by developing a framework in which the exported behavior of an e-Service is described in terms of its possible executions (execution trees). Then we specialize the framework to the case in which such exported behavior (i.e., the execution tree of the e-Service) is represented by a finite state machine. In this specific setting, we analyze the complexity of synthesizing a composition, and develop sound and complete algorithms to check the existence of a composition and to return one such a composition if one exists. To the best of our knowledge, our work is the first attempt to provide an algorithm for the automatic synthesis of e-Service composition, that is both proved to be correct, and has an associated computational complexity characterization.

When are two web services compatible

Whether two web services are compatible depends not only on static properties like the correct typing of their message parameters, but also on their dynamic behaviour. Providing a simple description of the service behaviour based on process-algebraic or automata-based formalisms can help detecting many subtle incompatibilities in their interaction. Moreover, this compatibility checking can to a large extent be automated if we define the notion of compatibility in a sufficiently formal way. Based on a simple behavioural representation, we survey, propose and compare a number of formal definitions of the compatibility notion, and we illustrate them on simple examples.

AUTOMATIC SERVICE COMPOSITION BASED ON BEHAVIORAL DESCRIPTIONS

This paper addresses the issue of automatic service composition. We first develop a framework in which the exported behavior of a service is described in terms of a so-called execution tree, that is an abstraction for its possible executions. We then study the case in which such exported behavior (i.e. the execution tree of the service) can be represented by a finite state machine (i.e. finite state transition system). In this specific setting, we devise sound, complete and terminating techniques both to check for the existence of a composition, and to return a composition, if one exists. We also analyze the computational complexity of the proposed algorithms. Finally, we present an open source prototype tool, called (E-Service Composer), that implements our composition technique. To the best of our knowledge, our work is the first attempt to provide a provably correct technique for the automatic synthesis of service composition, in a framework where the behavior of services is explicitly specified.

A Foundational Vision of e-Services

In this paper we propose a foundational vision of e-Services, in which we distinguish between the external behavior of an e-Service as seen by clients, and the internal behavior as seen by a deployed application running the e-Service. Such behaviors are formally expressed as execution trees describing the interactions of the e-Service with its client and with other e-Services. Using these notions we formally define e-Service composition in a general way, without relying on any specific representation formalism.

ComposingWeb Services with Nondeterministic Behavior

The promise of Web services is to enable the composition of new distributed applications/solutions: when no available service can satisfy a client request, (parts of) available services can be composed and orchestrated in order to satisfy such a request. Service composition involves two different issues: the synthesis, in order to synthesize, either manually or automatically, a specification of how coordinating the component services to fulfill the client request, and the orchestration, i.e., how executing the previous obtained specification by suitably supervising and monitoring both the control flow and the data flow among the involved services. In this work, we address the automatic composition synthesis when the behavior of the available services is non-deterministic, and hence is not fully controllable by the orchestrator. The service behavior is modeled by the possible conversations the service can have with its clients. The presence of nondeterministic conversations stems naturally when modeling services in which the result of each interaction with its client on the state of the service can not be foreseen

ESC : a tool for automatic composition of e -services based on logics of programs

In this paper we discuss an effective technique for automatic service composition and we present the prototype software that implements it. In particular, we characterize the behavior of a service in terms of a finite state machine. In this setting we discuss a technique based on satisfiability in a variant of Propositional Dynamic Logic that solves the automatic composition problem. Specifically, given (i) a client specification of his desired service, i.e., the service he would like to interact with, and (ii) a set of available services, our technique synthesizes the orchestration schema of a composite service that uses only the available services and fully realizes the client specification. The developed system is an open-source software tool, called (e-service composer), that implements our composition technique starting from services, each of them described in terms of a WSDL specification and a behavioral description expressed in any language that can capture finite state machines.