In Workflow Management Systems (WFMSs) safety of execution is a main need of more and more business processes and transactional workflows are real needs inside enterprizes. In previous works, transactional models consider mainly atomicity as the main issue regarding long term transactions. It rarely consider the fact that many processes may run concurrently and thus access and update the same data. Usually, the main isolation item is the data on which we apply locking approaches and this attitude don't worry about process dimension. In this work we study more precisely what are the real isolation needs in workflow environment. To realize these needs, we define "Isolation Spheres" inspired from "spheres of control" proposed by C. T. Davies to make a separation of concerns between workflow design and transactional properties specification.