MedTransact: Transaction Support for Mediation with Remote Service Providers Paulo F. Pires 1, 2 Louiqa Raschid 3 Abstract: There are many service providers that provide services on the internet via Web accessible servers. In order to effectively develop applications in this environment, it is important to provide a way to integrate these services so they can be used to built distributed applications. A system that integrates these services must deal with the dissimilar transaction capabilities of remote servers. In this paper, we present MedTransact, a mediator system that coordinates dissimilar service capabilities of remote service providers. MedTransact supports distributed transaction semantics across the mediator and the remote service providers. We describe the MedTransact architecture and discuss how distributed transactions are supported. Keywords: Distributed transaction management, mediator systems, transaction semantics. 1 CNPq – Brazil grant holder. 2 Computer Science Department – COPPE, Federal University of Rio de Janeiro, Brazil. E-mail: pires@cos.ufrj.br 3 Maryland Bussiness School and UMIACS, University of Maryland. E-mail: louiqa@umiacs.umd.edu 1. Introduction Wrapper mediator systems ([11],[15],[22],[29])have been successfully developed to mediate the query capability of remote (database or non-database) sources and to provide information integration at the mediator level. Typically these projects support transactions within the mediator but the transaction semantics is not extended to the remote services. Supporting a transaction service that is extended to the remote servers is critical if we wish to implement E-business services based on wrapper mediator systems. There has been extensive research in transaction support in distributed computing systems ([6],[7],[21],[25],[26],[27]) and in workflow management systems ([10],[14],[19],[23],[28]). While these projects address the support of distributed transactions, they do not consider mediating the service capabilities of autonomous remote service providers. This is a significant difference, since remote service providers will support dissimilar capabilities with respect to commit, and abort semantics. Thus, implementing a transaction semantics across the remote servers becomes much more difficult, compared to a scenario where all distributed components support identical transaction behavior. We note that current commercial E-business products ([13],[18]) are not able to mediate service providers with different transaction capabilities. MedTransact is an attempt to mediate dissimilar service capabilities of remote service providers, while supporting distributed transaction semantics across the mediator and the remote service providers. In this paper, we describe a motivating example of application semantics at the mediator level. It involves a travel agent negotiating with flight, hotel and car reservation services. This scenario is typical of current online E-business services. The example will illustrate the need to specify application level semantics and to implement distributed transaction semantics across the remote service providers. We then describe the MedTransact approach, and the three main contributions to support distributed transactions. The first is a language to specify remote service capability and to map remote service capability to a mediator service. The second contribution is to specify application semantics over the