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Web services have become popular as a vehicle for the design, integration, composition, reuse, and deployment of distributed and heterogeneous software. However, although industry standards for the description, composition, and orchestration of Web services have been under development, their conceptual underpinnings are not fully understood. Conceptual models for service specification are rare, as are investigations based on them. This paper presents and studies a multi-level service composition model that perceives service specification as going through several levels of abstraction. It starts from transactional operations at the lowest level and abstracts into activities at higher levels that are close to the service provider or end user. The authors treat service composition from a specification and execution point of view, where the former is about composition logic and the latter about transactional guarantees. Consequently, the model allows for the specification of a number of transactional properties, such as atomicity and guaranteed termination, at all levels. Different ways of achieving the composition properties and implications of the model are presented. The authors also discuss how the model subsumes practical proposals like the OASIS Business Transaction Protocol, Sun's WS-TXM, and execution aspects of the BPEL4WS standard. Keywords: Multi-Level Transactions, Service Composition, Service Orientation, Transactional-Properties, Web Service, INTRODUCTION Web services (Alonso et al., 2004; Casati & Dayal, 2002) have become popular as a vehicle for the design, integration, composition, reuse, and deployment of distributed and heterogeneous software, [...]

Web services are defined independently of any execution context. Due to their inherent autonomy and heterogeneity, it is difficult to examine the behaviour of composite services, especially in case of failures. This paper is interested in ensuring composite services reliability. Reliable composition is defined as a composition where all instance executions are correct from a transactional and business point of view. In this paper, the authors propose a transactional approach for ensuring reliable Web service compositions. The approach integrates the expressivity power of workflow models and the reliability of Advanced Transactional Models (ATM). This method offers flexibility for designers to specify their requirements in terms of control structure, using workflow patterns, and execution correctness. Contrary to ATM, the authors start from the designers' specifications to define the appropriate transactional mechanisms that ensure correct executions according to their requirements. Keywords: Advanced Transactional Models, Composite Services, Reliability, Web Services, Web Service Compositions, Workflow Patterns, INTRODUCTION The Web services approach (Erickson & Siau, 2008) has gained broad acceptance as a key technology to automate Business-to-Business (aka B2B) interactions. The Web services technology is an implementation [...]

The appropriate deployment of web service operations at the service provider site plays a critical role in the efficient provision of services to clients. In this paper, the authors assume that a service provider has several servers over which web service operations can be deployed. Given a workflow of web services and the topology of the servers, the most efficient mapping of operations to servers must then be discovered. Efficiency is measured in terms of two cost functions that concern the execution time of the workflow and the fairness of the load distribution among the servers. The authors study different topologies for the workflow structure and the server connectivity and propose a suite of greedy algorithms for each combination. Keywords: Composite Web Services, Service Providers, Service Provision, Web Services, Web Services Deployment, INTRODUCTION A web service is typically defined in the literature--for example, see Alonso, Casati, Kuno and Machiraju (2004)--as an interface that describes a collection of operations provided through the internet [...]

ABSTRACT The emergence of Web databases has introduced new challenges related to their organization, access, integration, and interoperability. New approaches and techniques are needed to provide across-the-board transparency for accessing […]