We present a goal-driven approach to model a choreographer for realizing composite Web services. In this framework, the users start with an abstract, and possibly incomplete functional specification of a desired goal service. This specification is used to compose a choreographer that allows communication between the client and the set of available component services, and is functionally equivalent to the goal service. However, if such a composition cannot be realized, the proposed approach identifies the cause(s) for the failure of composition. This information can be used by the user to minimally reformulate the goal to reduce the ‘gap between the desired functionality. The process can be iterated until a feasible composition is realized or the user decides to abort. The approach ensures that (i) a choreographer, if one is produced by our composition algorithm, in fact realizes the user-specified goal functionality; and (ii) the algorithm is guaranteed to find a composition that meets the user needs as captured in the goal specifications (whenever such a composition exists).

Abstract. A web service is modeled here as a finite state machine. A composition problem for web services is to decide if a given web service can be constructed from a given set of web services; where the construction is understood as a simulation of the specification by a fully asynchronous product of the given services. We show an EXPTIME-lower bound for this problem, thus matching the known upper bound. Our result also applies to richer models of web services, such as the Roman model.

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The promise of Web Service Computing is to use Web services as fundamental elements for realizing distributed applications/solutions. When no available service satisfies a desired specification, one might check whether (parts of) available services can be composed and orchestrated in order to realize the specification. The problem of automatic composition becomes especially interesting in the presence of conversational services. Among the various frameworks proposed in the literature, here we concentrate on the so called “Roman Model”, where: (i) each service is formally specified as a transition system that captures its possible conversations with a generic client; (ii) the desired specification is a target service, described itself as a transition system; (iii) the aim is to synthesize an orchestrator realizing the target service by exploiting execution fragments of available services. The Roman Model well exemplifies what can be achieved by composing conversational services and, also, uncovers relationships with automated synthesis of reactive processes in Verification and AI Planning. 1

Web services are rapidly emerging as the reference paradigm for the interaction and coordination of distributed business processes. In several research papers we have shown how advanced automated planning techniques can be exploited to automatically compose web services, and to synthesize monitoring components that control their execution. In this demo we show how these techniques have been implemented in the ASTRO toolset

Abstract. We ease the design of collaborative business processes respecting desired business goals by the composition algorithm presented in this paper. The composition of multiple parties ’ business processes is always done with a specific objective in mind. Not only in the positive case, but also if the objective of a business process can not be fulfilled, all participating business processes need to be in some expected recovery state. We propose a composition algorithm solving the task of designing a collaborative business process while respecting a set of primary and recovery goals. In our model, each business process is described as a finite state machine. The multiplication of all business processes in one single model of possible executions would lead to an explosion of the number of states. Therefore, our composition algorithm directly interprets the multiple finite state machine (FSM) representations and creates a collaborative business process without integrating all FSMs into one single FSM upfront. Our composition algorithm returns an orchestration of the given business processes only in the case that it can be assured that each execution only leads to an expected primary or recovery goal. In order to prove our concepts, we first mathematically define the execution of business processes and orchestrations by providing abstract state machine (ASM) representations for them. Second, we execute the ASMs in the execution engine CoreASM which shows that the generated orchestration steers the execution of the business processes as intended. 1

Abstract not found

Thanks to recent advances, AI Planning has become the underlying technique for several applications. Figuring prominently among these is automated Web Service Composition (WSC) at the “capability ” level, where services are described in terms of preconditions and effects over ontological concepts. A key issue in addressing WSC as planning is that ontologies are not only formal vocabularies; they also axiomatize the possible relationships between concepts. Such axioms correspond to what has been termed “integrity constraints ” in the actions and change literature, and applying a web service is essentially a belief update operation. The reasoning required for belief update is known to be harder than reasoning in the ontology itself. The support for belief update is severely limited in current planning tools. Our first contribution consists in identifying an interesting special case of WSC which is both significant and more tractable. The special case, which we term forward effects, is characterized by the fact that every ramification of a web service application involves at least one new constant generated as output by the web service. We show that, in this setting, the reasoning required for belief update simplifies to standard reasoning in the ontology itself. This relates to, and extends,

Abstract. In many practical applications, trade-offs involving non-functional attributes e.g., availability, performance play an important role in selecting component services in assembling a feasible composition, i.e., a composite service that achieves the desired functionality. We present TCP-Compose ⋆ , an algorithm for service composition that identifies, from a set of candidate solutions that achieve the desired functionality, a set of composite services that are non-dominated by any other candidate with respect to the user-specified qualitative preferences over non-functional attributes. We use TCP-net, a graphical modeling paradigm for representing and reasoning with qualitative preferences and importance. We propose a heuristic for estimating the preference ordering over the different choices at each stage in the composition to improve the efficiency of TCP-Compose ⋆. We establish the conditions under which TCP-Compose ⋆ is guaranteed to generate a set of composite services that (a) achieve the desired functionality and (b) constitute a non-dominated set of solutions with respect to the user-specified preferences and tradeoffs over the nonfunctional attributes. 1

In this paper we look at the problem of composing services that export their behavior in terms of a transition system, characterizing the choices of actions given to a client at each point in time. The composition consists of synthesizing an orchestrator that coordinates the available services so as to mimic the desired target service asked by the client. Specifically, in this paper we study the “conformant form ” of the problem, where available services are partially controllable and partially observable, and hence, the orchestrator has to make its decisions exploiting the observations made so far only. We give a sound and complete procedure to synthesize the orchestrator in such case, and characterize the computational complexity of the problem. The procedure is based on working with belief (or knowledge) states, a standard technique to tackle conformant planning. Moreover we show that, although in general unavoidable, the powerset construction at the base of the belief state approach can be delegated to the symbolic manipulations of the game-structure model checking tool (TLV), which can be used to efficiently implement the orchestrator synthesis procedure.