Reasoning about Actions for e-Service Composition

In the world of Service Oriented Architectures, one deals with networks of cooperating components. A component offers services; to deliver a service it possibly needs services of other components, thus forming a service tree. This tree is built dynamically and not known beforehand. It is hard to verify the behavior of a service tree by using standard verification techniques, because these techniques typically assume a static flattened model. In this paper we model a component by an open Petri net. We give a sufficient condition for proper completion (called soundness) that requires only pairwise checks of the service compositions. We also provide a correctness-by-construction approach for building services trees.

Up to now, research on e-Services has mainly concentrated on the issues of (i) service description and modeling and of (ii) service composition, including synthesis and orchestration.

2008

The paper investigates fundamental decision problems and composition synthesis for Web services commonly found in practice. We propose a notion of synthesized Web services (SWS's) to specify the behaviors of the services. Upon receiving a sequence of input messages, an SWS issues multiple queries to a database and generates actions, in parallel; it produces external messages and database updates by synthesizing the actions parallelly generated. In contrast to previous models for Web services, SWS's advocate parallel processing and (deterministic) synthesis of actions. We classify SWS's based on what queries an SWS can issue, how the synthesis of actions is expressed, and whether unbounded input sequences are allowed in a single interaction session. We show that the behaviors of Web services supported by various prior models, data-driven or not, can be specified by different SWS classes. For each of these classes we study the non-emptiness, validation and equivalence problems, and establish matching upper and lower bounds on these problems. We also provide complexity bounds on composition synthesis for these SWS classes, identifying decidable cases.

2003

Abstract Composition of e-Services is the issue of synthesizing a new composite e-Service, obtained by combining a set of available component e-Services, when a client request cannot be satisfied by available e-Services. In this paper we propose a general framework addressing the problem of e-Service composition. We then show that, under certain assumptions, composition can be realized through DL-based reasoning.

We study the problem of automatic web service composition. We consider a formal framework where web service business protocols are described by means of Finite State Machines (FSM) and focus on the protocol synthesis problem. We show that this problem can be reduced to that of testing a simulation relation between an FSM and an (innitely) iterated product of FSMs. While this later problem has never been investigated in the literature, existing results regarding close decision problems in the context of shue languages, an extension of regular languages with shue and shue closure operators, are rather negative and cannot be directly exploited in our context. In this paper, we develop a novel technique to prove the decidability of testing simulation in the case of interest in our setting. As a consequence, our results solve the problem of web service composition (synthesis) existence in presence of an unbounded number of instances, a problem left open in recent related works.

Electronic Notes in Theoretical Computer Science, 2010

Composition of Web services consists of the interleaving of the sequence of actions executed by the elementary services in accordance with a client specification. We model Web services as automata executing actions and also sending and receiving messages. This paper provides a theoretical study for three service composition problems, and in particular for the problem of computing a Boolean formula which exactly characterises the conditions required for services to answer the client's request. New complexity results are established for these problems within the framework of service composition with constraints.

We present a consistency-based service composition approach, where composition problems are modelled in a generic manner using a generative constraint-based formalism. We show that in our framework concise formal specification of service configuration problems is possible. Preliminary results indicate that our approach is scalable and competitive with other state-of-the-art composition systems.

International Workshop on Scalable and Usable Model Checking for Petri Nets and other models of concurrency, 2010

Abstract. Automating the composition of web services is an object of a growing interest nowadays. In our former paper [3] we proposed a method for converting the problem of the composition to the problem of building a graph of worlds consisting of formally defined objects, and presented the first phase of this composition resulting in building a graph of types of services (an abstract graph). In this work we propose a method of replacing abstract flows of this graph by sequences of concrete services able to satisfy the user's request. ...

International Journal …, 2005

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 socalled 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 ESC (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. In general, the client can either be a human or another service. In what follows, we refer to the client with the "he" pronoun, in order to avoid confusion when referring to the services and to its clients using the pronouns. However, the reader should remember that we could as well as use the "it" pronoun for the client.