A Modeling Perspective on Web Service Contracting Steffen Lamparter 1 Sibylle Mutschler 2 Stefan Luckner 3 Kendra Stockmar 2 Carolina M. Laborde 2 1 Institute AIFB, University of Karlsruhe (TH), Germany http://www.aifb.uni-karlsruhe.de/WBS 2 Institute for Information Law, University of Karlsruhe (TH), Germany http://www.zar.uni-karlsruhe.de/zar 3 Chair for Information Management and Systems, University of Karlsruhe (TH), Germany http://www.iw.uni-karlsruhe.de Abstract Service-oriented computing as a concept for providing interoperability and flexibility within heterogeneous envi- ronments has gained much attention within last years. Dy- namically integrating external Web services into enterprise applications requires automatic contracting between ser- vice requestors and providers. Admittedly, pure automatic contracting is currently not feasible due to the complexity of real world contracts. As an interim solution we aim towards semi-automatic contracting where some clauses are negotiated automatically within the scope of a frame- work contract. In this paper, we elaborate on the content of Web service contracts from a legal perspective before discussing an ontology-based representation of negotiable contract clauses. 1 Introduction Information systems of the future will be combinations of loosely-coupled services. One can observe an obvi- ous trend towards service-oriented architectures (SOA). In SOA, applications are assembled as required by pulling to- gether various services. In this context, a service is a soft- ware component which can be used by means of standard internet technologies. The implementation of services is en- capsulated and numerous service providers may provide the same functionality. Hence, a service requestor may choose from a variety of implementations depending on his prefer- ences. So as to make sure that an appropriate service will be provided, service requestors and providers have to agree on terms of a contract. According to [8] such a contracting process can be characterized by three phases: (1) Information Phase: In this phase market participants gather information about the general business environment, potential business partners, and products or services. (2) Agreement Phase: In this phase the terms of trade are negotiated and a legally binding contract is closed between the participants. (3) Settlement Phase: In the Settlement Phase the busi- ness actions agreed in the contract are carried out. Since SOA aims at dynamic discovery and invocation of services during run-time, the contracting process cannot be done by human beings but rather has to be done by the sys- tem itself. Thus, machine-understandable information is re- quired to enable the system to interpret, understand, and use this information. In the Information Phase concrete or- ders have to be derived from market information. This can only be done if information about goods, market partici- pants, etc. is available in a formalized and thus machine- understandable form. In order to facilitate dynamic match- making and negotiation in the Agreement Phase formaliza- tion of requests and offers is required. Machine-readable contracts also facilitate contract exe- cution and monitoring in the Settlement Phase. They allow for adapting services to a contract reached. To give an ex- ample, the computing power made available for a certain service request can be adjusted depending on the average response time guaranteed in the contract. Additionally, they can be used to check whether a contract is met or not. Such automated contract enforcement can only be realized if con- tracts can be interpreted by software. In this paper, we mainly focus on the Agreement Phase. In doing so, we concentrate on the content of Web service contracts and the formalization of this content. We do not address dynamic aspects, like negotiation protocols or other interactions that may lead to contracts. Our paper is structured as follows. In section 2, we pro-