Emerging service oriented architecture is increasing the evolution and variation of software resources. Applications that cannot adapt to dynamic environments will decrease their usefulness, particularly to business process management systems that face requirements changed frequently. In response to the realistic requirements, this paper, based on Web services and business process management techniques, propose a model of service cooperation middleware (SCM) for enterprise computing. First, it discusses the conceptual architecture and operation mechanisms of SCM, then formalizes the meta-model of cooperative processes deployed on SCM. By introducing a model transformation function into the formalization, a static process model can be extended to a dynamic one. In virtue of the reflection capability, structural reconstruction and behavioral adaptation of the dynamic processes can be achieved in SCM by introspection and effectuation. In terms of the conceptual model of SCM, a process virtual machine (PVM) is designed as a running container for cooperative processes. Borrowed from the power of MDA mechanism, the model of a business process can be transformed successively from design to run time. The business processes established on SCM can be more flexibly and extensively applied to various open environments, and leverage modern enterprise computing.