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.

• Paulo F. Pires, Marta L.Q. Mattoso, Mário Roberto F. Benevides, Coordenação de Transações em Ambientes de Serviços Web. IX Simpósio Brasileiro de Sistemas Multimídia e Web (WebMídia 2003). To appear.
• Paulo F. Pires, Marta L.Q. Mattoso, Mário Roberto F. Benevides, Building Reliable Web Services Compositions. Web, Web-Services, and Database Systems 2002. Springer LNCS 2593, ISBN 3-540-00745-8, pp. 59-72, 2003. ( a short description of the framework )
• Paulo F. Pires, Marta L.Q. Mattoso, Mário Roberto F. Benevides, Mediating Heterogeneous Web Services. SAINT 2003, pp 344-347, IEEE Computer Press.
• Valdino Azevedo, Paulo F. Pires, Marta Mattoso, 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).
• da Costa, L. A. G., Pires, P. F., Mattoso, M. (2004):
  Automatic Composition of Web Services with Contingency Plans,
  IEEE International Congress on Web Services - ICWS 2004,
  San Diego, CA, USA, July.
• da Costa, L. A. G., Pires, P. F., Mattoso, M. (2004):
  WebComposer: a Tool for the Composition and Execution of Web Service-based Workflows,
  10th Brazilian Symposium on Multimedia and the Web - LA-WebMedia 2004,
  IEEE CS Press, Ribeirão Petro, SP, Brasil, Outubro.  

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 Web services composition. Under development by Luiz Gibson Costa.
  The semantic Web technology and the Web services description language extensibility may be combined to describe services in an unambiguous and machine interpretable way, automating Web services discovery, selection and invocation. In this activity, we present an algorithm and a prototype for the automatic composition of Web services that implement workflows described in a high level language. Our approach has many advantages comparing to the manual creation of a simple program composition, such as smaller implementation time and cost, reliability with the generation of contingency plans, greater capacity to evolve with the dynamic service discovery, and faster execution time with the use of heuristics. We use the OWL-S ontology to semantically describe Web services metadata and indexes to help selecting them. The proposed algorithm considers that equivalent services may have different interfaces and also respects preferences of the users. Publications (Description in Portuguese)

• Valdino Azevedo, Paulo F. Pires, Marta L.Q. Mattoso, WebTransact-EM: Um Modelo para a Execução Dinâmica de Serviços Web Semanticamente Equivalentes. IX Simpósio Brasileiro de Sistemas Multimídia E Web (WebMídia 2003). To appear.

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.