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

Web service substitution refers to the problem of identifying a service that can replace another service in the context of a composition with a specified functionality. Existing solutions to this problem rely on detecting the functional and behavioral equivalence of a particular service to be replaced and candidate services that could replace it. We introduce the notion of context-specific substitutability, where context refers to the overall functionality of the composition that is required to be maintained after replacement of its constituents. Using the context information, we investigate two variants of the substitution problem, namely environment-independent and environmentdependent, where environment refers to the constituents of a composition and show how the substitutability criteria can be relaxed within this model. We provide a logical formulation of the resulting criteria based on model checking techniques as well as prove the soundness and completeness of the proposed approach.

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. 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.

We study the problem of synthesis of a choreogrpher in Web service composition for a given set of services and a goal. Services and goal are represented using i/o automata which can succinctly and precisely describe the interfaces of the services. Our technique considers existence and synthesis of two types of the choreographers: a simple choreographer capable of only relaying outputs from one service to input of another and a transducing choreographer which is capable of storing and reusing inputs/outputs from the services. The central theme of our technique relies on generating i/o automata representation of all possible choreographed behavior of existing services (captured in form of universal service automaton, a concept introduced in this paper) and verifying that the goal can be simulated by the universal set of choreographed behaviors. 1

Typical approaches to service composition seek to realize a goal service specification, described using a labeled transition system (LTS) provided by a service developer, by constructing a structurally equivalent LTS using a set of available component services (also described using LTSs) that match the input and output requirements of the transitions. As such, existing composition approaches fail to realize the goal LTS whenever available component service LTSs cannot be used to “mimic ” the structure of the goal LTS. This failure requires that the service developer formulates an alternate goal LTS and re-iterates the composition step. However, the process of manual reformulation of the goal LTS is both laborious and error prone. In this setting, we describe an efficient data structure and algorithms for analyzing data and control flow dependencies implicit in a user-supplied goal LTS specification to automatically generate alternate LTS specifications that capture the same overall functionality with respect to the data and control dependencies, and determine whether any of the alternatives can lead to a feasible composition. The result is a significant reduction in the need for the tedious manual intervention in reformulating LTS specifications of the goal service. 1

Customizing web services according to users’ individual functional and non-functional requirements has become increasingly difficult as the number of users increases. This paper introduces a new way to customize and verify composite web services by incorporating a software product-line engineering approach into web-service composition. The approach uses a partitioning similar to that between domain engineering and application engineering in the product-line context. It specifies the options that the user can select and constructs the resulting webservice compositions. By first creating a web-service composition search space that satisfies the common requirements and then querying the search space as the user selects values for the parameters of variation, we provide a more efficient way to customize web services. A decision model, illustrated with examples from an emergency-response application, is created to interact with the customers and ensure the consistency of their specifications. The capability to reuse the composition search space may also help improve the quality and reliability of the composite services and reduce the cost of re-verifying the same compositions. 1.

Typical approaches to service composition seek to realize a goal service specification, described using a labeled transition system (LTS) provided by a service developer, by constructing a structurally equivalent LTS using a set of available component services (also described using LTSs) that match the input and output requirements of the transitions. As such, existing composition approaches fail to realize the goal LTS whenever available component service LTSs cannot be used to “mimic ” the structure of the goal LTS. This failure requires that the service developer formulates an alternate goal LTS and re-iterates the composition step. However, the process of manual reformulation of the goal LTS is both laborious and error prone. In this setting, we describe an efficient data structure and algorithms for analyzing data and control flow dependencies implicit in a user-supplied goal LTS specification to automatically generate alternate LTS specifications that capture the same overall functionality with respect to the data and control dependencies, and determine whether any of the alternatives can lead to a feasible composition. The result is a significant reduction in the need for the tedious manual intervention in reformulating LTS specifications of the goal service. 1