In this paper, we are interested in structured cooperation based on workflow (WF). The current work proposes an approach based on services for WF interconnection particularly obeying to the "case transfer" architecture. This late defines a form of cooperation in Inter-Organizational WF involving a range of partners with common business goals, exercising the same business. All partners share the same WF model implemented at each location and a transfer policy to manage transfer for process instances from one partner to another. By the use of services, our goal is to obtain IOWF models flexible enough so they remain easily adaptable to support process changes. The proposed approach is based on centralized control for transfers.