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. We propose an approach for incremental modeling of composite Web services. The technique takes into consideration both the functional and nonfunctional requirements of the composition. While the functional requirements are described using symbolic transition systems—transition systems augmented with state variables, function invocations, and guards; non-functional requirements are quantified using thresholds. The approach allows users to specify an abstract and possibly incomplete specification of the desired service (goal) that can be realized by selecting and composing a set of pre-existing services. In the event that such a composition is unrealizable, i.e. the composition is not functionally equivalent to the goal or the non-functional requirements are violated, our system provides the user with the causes for the failure, that can be used to appropriately reformulate the functional and/or non-functional requirements of the goal specification. 1

Abstract. In electric power transmission systems, the assets include transmission lines, transformers, power plants and support structures. Maintaining these assets to reliably deliver electric energy at low prices is critical for a nation’s growth and development. Towards this end, we describe a novel service-oriented architecture for sensing, information integration, risk assessment, and decisionmaking tasks that arise in operating modern high-voltage electric power systems. The proposed framework integrates real-time data acquisition, modeling, and forecasting functionalities provided by relatively autonomous, loosely coupled entities that constitute the power industry to determine operational policies, maintenance schedules and facility reinforcement plans required to ensure reliable operation of power systems. 1

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

Abstract. We propose a new framework for modeling Web services based on the techniques of abstraction, composition and reformulation. The approach allows users to specify an abstract and possibly incomplete specification of the composite (goal) service. This specification is used to select a set of suitable component services such that their composition realizes the desired goal. In the event that such a composition is unrealizable, the cause for the failure of composition is determined and is communicated to the user thereby enabling further reformulation of the goal specification. This process can be iterated until a feasible composition is identified or the user decides to abort. 1

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We propose a specification-driven approach to Web service composition. Our framework allows the users (or service developers) to start with a high-level, possibly incomplete specification of a desired (goal) service that is to be realized using a subset of the available component services. These services are represented using labeled transition systems augmented with guards over variables with infinite domains and are used to determine a strategy for their composition that would realize the goal service functionality. However, in the event the goal service cannot be realized using the available services, our approach identifies the cause(s) for such failure which can then be used by the developer to reformulate the goal specification. Thus, the technique supports Web service composition through iterative reformulation of the functional specification. We present a prototype implementation in a tabled-logic programming environment that illustrates the key features of the proposed approach. Keywords: Service-oriented architectures; web services; composition; symbolic transition systems; tabled-logic programming. 109 110 J. Pathak et al. 1.

In many applications involving composite Web services, one or more component services may become unavailable. This presents us with the problem of identifying other components that can take their place, while maintaining the overall functionality of the composite service. Given a choice of candidate substitutions that offer the desired functionality, it is often necessary to select the most preferred substitution based on non-functional attributes of the service, e.g., security, reliability, etc. We propose an approach to this problem using preference networks for representing and reasoning about preferences over non-functional properties. We present algorithms for solving several variants of this problem: a) when the choice of the preferred substitution is independent of the other constituents of the composite service; b) when the choice of the preferred substitution depends on the other constituents of the composite service; and c) when multiple constituents of a composite service need to be replaced simultaneously. The proposed solutions to the service substitution problem based on preferences over non-functional properties are independent of the specific formalism used to represent functional requirements of a composite service as well as the specific algorithm used to assemble the composite service. 1.

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