The Web services technology provides the underpinning to a new business opportunity, i.e., the possibility of providing value-added services through the composition of basic Web services. However, at its present stage, the Web services technology does not provide the necessary tools to build Web service compositions. The current Web services technology provides the necessary communication model for enabling message exchanges in the Web services environment. However, communication interoperability is only part of the problem when considering the building of reliable Web services compositions. Besides communication interoperability, the task of building Web service compositions requires mechanisms to deal with the inherent autonomy, and heterogeneity of Web services.

In this work, we present a framework, named WebTransact, which provides the necessary infrastructure for building reliable, maintainable, and scalable Web service compositions. The WebTransact framework is composed of a multilayered architecture, an XML-based language, and a transaction model. The multilayered architecture of WebTransact separates the task of aggregating and homogenizing heterogeneous Web services from the task of specifying transaction interaction patterns, thus providing a new general mechanism to deal with the complexity introduced by a large number of Web services. The XML-based language, named Web Service Transaction Language (WSTL), is used for describing the transaction support and the content of Web services, for defining the aggregation rules of Web services, and for specifying the transaction interaction patterns of compositions. WSTL is an extension of WSDL thus it is adherent to the XML-based standards that enable Web service technology. The transaction model provides the adequate correctness guarantees when executing Web services compositions built with WSTL. The transaction model of WebTransact uses a new correctness criterion, named 2L-guaranteed-termination, which is a weaker notion of atomicity that considers the needs of Web service environments. Still, we have developed formal definitions for reasoning on safe and correct execution of Web services compositions built with the mechanisms provided by the WebTransact framework. Use cases demonstrating the usage and potential of WebTransact are presented.

• Building Reliable Web Services Compositions. Web, Web-Services, and Database Systems 2002. Springer LNCS 2593, ISBN 3-540-00745-8, pp. 59-72, 2003. Paulo F. Pires, Marta L.Q. Mattoso, Mário Roberto F. Benevides. ( a short description of the framework )
• Mediating Heterogeneous Web Services. SAINT 2003, pp 344-347, IEEE Computer Press. Paulo F. Pires, Marta L.Q. Mattoso, Mário Roberto F. Benevides.
• Handling Dissimilarities of Autonomous and Equivalent Web Services. Caise 2003 Workshop on "Web Services, e-Business, and the Semantic Web (WES): Foundations, Models, Architecture, Engineering and Applications" (to appear). Valdino Azevedo, Paulo F. Pires, Marta Mattoso
• WebTransact: Coordinating, Composing and Mediating Web Services. IEEE Computer, Special Issue on Web Services Computing. Submitted in January 2003. Selected to the second evaluation round in March 2003.Paulo F. Pires, Marta L.Q. Mattoso, Mário Roberto F. Benevides.

The Complete Specification:

• Pires, P.F., “WebTransact: An Infrastructure for Building Reliable Web Services Compositions”. Doctoral Thesis, COPPE/UFRJ, Brasil, Rio de Janeiro, July 2002.

Current Activities

• Implementation of the WebTransact execution model using EJB components. Under development as an undergraduate final project at the Computer Science Department of UFRJ (Description in Portuguese)
• Implementation of a Web service transaction service based on the WebTransact concepts. Under development as an undergraduate final project at the Computer Science Department of UFRJ (Description in Portuguese)

The complete specification (In portuguese):

• AZEVEDO, V., “WebTransact-EM: Um Modelo para a Execução Dinâmica de Serviços Web Semanticamente Equivalentes”. Master Thesis, COPPE/UFRJ, Brasil, Rio de Janeiro, 2003.

We expect to have publications in english on this subject soon.