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Service-oriented architectures (SOA) is an emerging approach that addresses the requirements of loosely coupled, standards-based, and protocol- independent distributed computing. Typically business operations running in an SOA comprise a number of invocations of these different components, often in an event-driven or asynchronous fashion that reflects the underlying business process needs. To build an SOA a highly distributable communications and integration backbone is required. This functionality is provided by the Enterprise Service Bus (ESB) that is an integration platform that utilizes Web services standards to support a wide variety of communications patterns over multiple transport protocols and deliver value-added capabilities for SOA applications. This paper reviews technologies and approaches that unify the principles and concepts of SOA with those of event-based programing. The paper also focuses on the ESB and describes a range of functions that are designed to offer a manageable, standards-based SOA backbone that extends middleware functionality throughout by connecting heterogeneous components and systems and offers integration services. Finally, the paper proposes an approach to extend the conventional SOA to cater for essential ESB requirements that include capabilities such as service orchestration, "intelligent" routing, provisioning, integrity and security of message as well as service management. The layers in this extended SOA, in short xSOA, are used to classify research issues and current research activities.

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Service oriented architectures: approaches, technologies and research issues

Service-oriented computing

Taverna is an application that eases the use and integration of the growing number of molecular biology tools and databases available on the web, especially web services. It allows bioinformaticians to construct workflows or pipelines of services to perform a range of different analyses, such as sequence analysis and genome annotation. These high-level workflows can integrate many different resources into a single analysis. Taverna is available freely under the terms of the GNU Lesser General Public License (LGPL) from http://taverna.sourceforge.net/.

Taverna: a tool for building and running workflows of services

Recent technology trends in the Web Services (WS) domain indicate that a solution eliminating the presumed complexity of the WS-* standards may be in sight: advocates of REpresentational State Transfer (REST) have come to believe that their ideas explaining why the World Wide Web works are just as applicable to solve enterprise application integration problems and to simplify the plumbing required to build service-oriented architectures. In this paper we objectify the WS-* vs. REST debate by giving a quantitative technical comparison based on architectural principles and decisions. We show that the two approaches differ in the number of architectural decisions that must be made and in the number of available alternatives. This discrepancy between freedom-from-choice and freedom-of-choice explains the complexity difference perceived. However, we also show that there are significant differences in the consequences of certain decisions in terms of resulting development and maintenance costs. Our comparison helps technical decision makers to assess the two integration styles and technologies more objectively and select the one that best fits their needs: REST is well suited for basic, ad hoc integration scenarios, WS-* is more flexible and addresses advanced quality of service requirements commonly occurring in enterprise computing.

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Restful web services vs. "big"' web services: making the right architectural decision

Like many other incipient technologies, Web services are still surrounded by a substantial level of noise. This noise results from the always dangerous combination of wishful thinking on the part of research and industry and of a lack of clear understanding of how Web services came to be. On the one hand, multiple contradictory interpretations are created by the many attempts to realign existing technology and strategies with Web services. On the other hand, the emphasis on what could be done with Web services in the future often makes us lose track of what can be really done with Web services today and in the short term. These factors make it extremely difficult to get a coherent picture of what Web services are, what they contribute, and where they will be applied.Alonso and his co-authors deliberately take a step back. Based on their academic and industrial experience with middleware and enterprise application integration systems, they describe the fundamental concepts behind the notion of Web services and present them as the natural evolution of conventional middleware, necessary to meet the challenges of the Web and of B2B application integration. Rather than providing a reference guide or a "how to write your first Web service" kind of book, they discuss the main objectives of Web services, the challenges that must be faced to achieve them, and the opportunities that this novel technology provides. Established, as well as recently proposed, standards and techniques (e.g., WSDL, UDDI, SOAP, WS-Coordination, WS-Transactions, and BPEL), are then examined in the context of this discussion in order to emphasize their scope, benefits, and shortcomings. Thus, the book is ideally suited both for professionals considering the development of application integration solutions and for research and students interesting in understanding and contributing to the evolution of enterprise application technologies.

Web Services: Concepts, Architectures and Applications

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Service-Oriented Computing - ICSOC 2005

In the traditional application model, services are tightly coupled with the processes they support. For example, whenever a server’s process changes, existing clients using that process must also be updated. However, electronic commerce is moving toward e-service based interactions, where corporate enterprises use e-services to interact with each other dynamically, and a service in one enterprise could spontaneously decide to engage a service fronted by another enterprise. We clarify here the relationship between currently developing standards such as UDDI, WSDL, and WSCL, and propose a conversation controller mechanism that leverages such standards to direct services in their conversations. We can thus treat services as pools of methods, independent of the conversations they support. Even method names can be decided on independently of the conversations. Services can spontaneously discover each other and then engage in complicated interactions without the services themselves having to explicitly support conversational logic. The dynamism and flexibility enabled by this decoupling is the essential difference between applications offered over the web and e-services.

Technologies for E-Services

Web services are emerging technologies for integrating heterogeneous applications. In application integration, the internal services are interconnected with other external resources to form a virtual enterprise. This puts new requirements on the standardization in terms of external specification, i.e., a combination of service interfaces and business protocols, that interconnected services have to obey. However, previously developed service implementations do not always conform to the standard and require adjustment.

In this paper, we characterize the problem of aligning internal service implementation to a standardized external specification. We propose an Aspect oriented framework as a solution to provide support for service adaptation. In particular, the framework consists of i) a taxonomy of the different possible types of mismatch between external specification and service implementation, ii) a repository of aspect-based templates to automate the task of handling mismatches, and iii) a tool to support template instantiation and their execution together with the service implementation.

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An aspect-oriented framework for service adaptation

Web services are increasingly gaining acceptance as a framework for facilitatingapplication-to-application interactions within and across enterprises. They pro-videabstractionsandtechnologiesforexposingenterpriseapplicationsasservicesand make them accessible programmatically through standardized interfaces.However, tools supporting service development today provide little support forhigh level modeling and analysis of abstractions at higher level of services stack,and in particular there is little support for protocol modeling and management.We believe that indeed protocol modeling and management will be key in sup-porting Web service development and interaction, and that developing formalmodels and a protocolalgebra will have a positive impact similar to the one thatthe relational model and the relational algebra had in database technology.Whendeveloping ourframeworkfor serviceprotocolsmodeling, analysis,andmanagement [1,2], we identiﬁed the need for representing temporal abstractionsin protocol descriptions. In particular, our analysis of the characteristics and re-quirements of service protocols in terms of description languages, we found that,inadditiontomessagechoreographyconstraints,protocolspeciﬁcationlanguagesneed to cater for time-sensitive conversations(i.e., conversationsthat arecharac-terized by temporal constraints on when an operation must or can be invoked).For example, a protocolmay specify thatapurchase ordermessageis acceptedonly if it is received within 24 hours after a quotation has been received. In thispaper, we discuss the augmentation of business protocols with speciﬁcations oftemporal abstractions (called timed protocols). Then we motivate, through ex-amples, a need for analyzing timed protocol speciﬁcations, and speciﬁcally foridentifying if and under what conditions two services, characterized by certaintimed protocols, can interact. Technical details are given in an extended versionof this paper [3] where a formal timed business protocol model is presented andoperators that enable characterizing compatibility and replaceability classes fortimed protocols are described.

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Fabio Casati

Papers

Web Services: Concepts, Architectures and Applications

Service-Oriented Computing - ICSOC 2005

Technologies for E-Services

An aspect-oriented framework for service adaptation

On Temporal Abstractions of Web Service Protocols