Abstract
Specifying a complex system, such as workflow applications, is a difficult task, which can not be done in one step. The stepwise refinement technique. facilitates the understanding of complex systems by dealing with the major issues before getting involved in the details. This papers presents a refinement based modelling approach of workflow Applications using UML Activity Diagrams. The proposed approach allows an incrementally developing more and more detailed models, preserving correctness in each step. We provide formal support for building process refinement graphs that are completely proved correct. We illustrate, as well, the proposed technique through an example of workflow application specified by our developed tool supporting the approach. This tool assists the developer in the task of refinement steps.