108 Jens Hündling and Mathias Weske  Web Services: Foundation and Composition Web Services: Foundation and Composition JENS HÜNDLING AND MATHIAS WESKE Keywords: Web services, Web services composition, Service Oriented Architecture A b s t r a c t Today both business analysts and informa- tion systems engineers attribute a great potential to Web services as a vehicle to simplify the interoperability of services offered by different organizations in elec- tronic business scenarios. In this paper, the Service Oriented Architecture is explained as the foundation of this new technology. The main implications and benefits of this architecture and the new possibilities offered are discussed. Since standards play an increasingly important role in this new technology, new and upcoming standards for an implementation of this architecture are summarized; these combined standards are known as Web services technology. Since the real potential for Web services is facilitating business processes, a recently specified framework for defining and executing business processes in a Web services envi- ronment is presented. Rather than solely discussing the strategic benefits of Web services, this paper also tries to point out current technological deficiencies and recent approaches to overcome them. A u t h o r s Mathias Weske (weske@hpi.uni-potsdam.de) is a Professor of Computer science at the Hasso Plattner Institute for Software Systems Engineering at the University of Potsdam, Germany, where he leads a business process technology research group. His current research interests include workflow management, case handling, Product Family Engineering, and web services technology. He is a member of the GI, vice chair of the executive committee of GI SIG EMISA, and a member of IEEE and ACM. Jens Hündling (huendling@hpi.uni-potsdam.de) is a Research Assistant in a business process technology group at the Hasso Plattner Institute for Software Systems Engineering at the University of Potsdam. His research interests include workflow management and B2B information integration using Web services technology. SPECIAL SECTION: WEB SERVICES SERVICE ORIENTED ARCHITECTURE PARADIGM The paradigm shift from product- to service-oriented information systems and infrastructure is currently shaking the markets both from an economic and technical point of view. Today, information systems are often com- panies’ core assets in their attempts to reach their goals of offering and selling products and services in an increasingly competitive market envi- ronment. However, the requirements of today’s dynamic business scenarios on the one hand and tight software budgets of many players on the other hand in many cases render inadequate development of infor- mation systems from scratch. Instead, assembling information systems from existing software components is the way to go. These software compo- nents can be specified as services. On an abstract level, business applications are built from local services and ser- vices provided by other companies. In this paper we will explain the principles of an architecture support- ing these requirements and – at the same time – the evolution of a new paradigm: The Service Oriented Architecture (SOA) (Burbeck 2000). To make this abstract architecture more concrete, we describe a current implementation of the SOA, based on Web services technology. The Service Oriented Architecture is another approach and – as will be detailed in this paper – a promising approach in the struggle of build- ing reusable software components (Leymann et al. 2002). This evolution started with the idea of functional decomposition, i.e. breaking down a large system into distinct parts. This approach led to application programming interfaces as a collec- tion of operation descriptions. Object orientation was the next concept; it encapsulated data and functionality as logical units of objects and classes to simplify software reuse. Service orientation is often seen as a new paradigm (Burbeck 2000, Mohan 2002). Organizations are offering services, implemented by a variety of software components. As we will see in the second part of the paper, services can be composed to reflect business processes, which in turn can be offered as a single service afterwards. In a SOA, functionality of software systems is provided by services. Organ- izations may use services offered by other companies, and companies may provide services to the market. In addition, information systems may use a variety of services to produce additional, higher-level services. The key requirements of this scenario are as follows: • Service description: The ability to describe services in a standard- ized way, so that potential users of a given service have sufficient information to decide to use the service. DOI: 10.1080/1019678032000067226 Copyright  2003 Electronic Markets Volume 13 (2): 108–119. www.electronicmarkets.org Downloaded By: [Schmelich, Volker] At: 14:52 16 March 2010