Event Based Web Service Description and Coordination Wilfried Lemahieu, Monique Snoeck, Cindy Michiels, Frank Goethals, Guido Dedene, Jacques Vandenbulcke Katholieke Universiteit Leuven, Department of Applied Economic Sciences, Naamsestraat 69, B-3000 Leuven, Belgium {wilfried.lemahieu, monique.snoeck, cindy.michiels, frank.goethals, guido.dedene, jacques.vandenbulcke}@econ.kuleuven.ac.be Abstract. This paper proposes the concept of business events as the cornerstone to web service description and coordination. First, a web service architecture is introduced as the result of an event based analysis & design phase. Then, it is advocated how the event concept can be used for semantically rich web service description. A distinction is made between two web service interfaces: a non-transactional query interface and a transactional event notification interface. Furthermore, a web service composition model is proposed, based on event broadcasting and event preconditions, instead of traditional one-to-one method invocations. The composition model is presented in a static variant and in a version with dynamic subscription. Throughout the paper, it is shown how the event based approach fits entirely within the current standard SOAP/WSDL/UDDI web services stack. 1 Introduction The web services concept can be considered as a revolutionary paradigm for loosely coupled application integration within and across enterprise boundaries. It promises to bring about a revolution in the way business partners can integrate their information systems, allowing for innovative organizational forms that were unthinkable before [1]. A web service can be looked upon as a public, remote interface to certain functionality, where the actual implementation is hidden from the applications that use it. In this aspect it is very similar to distributed object technologies such as RMI, CORBA and DCOM, which are, however, restricted to the intranet. In contrast, web services use a lightweight XML messaging protocol, SOAP [2], which is applicable across the entire Internet, without being hampered by companies’ firewalls. Still, despite its obvious great promises, the web service paradigm hasn’t fully lived up to its expectations (yet), at least not at the inter-enterprise level. Indeed, web services are well established for intra-enterprise application integration (EAI) and even static business-to-business interaction (B2Bi), i.e. in an extended enterprise with fixed, long-standing business partners. However, they fail to provide more than very basic services at the level of dynamic B2Bi, where services dynamically find one another and enter ad-hoc partnerships to perform complex business transactions.