Due to increased complexity and flexibility of processes and lack of modelling information, workflow processes are not always defined completely before their execution. Support for incompletely specified processes which require on-the-fly articulation of processes has become a desirable feature of workflow management systems. Unfortunately, this aspect is rather weak in contemporary workflow research. This paper reports innovative research on incompletely specified process support carried out in the context of SwinDeW, a peer-to-peer based decentralised workflow system. In order to extend the SwinDeW architecture and system functions seamlessly for supporting incompletely specified processes, a hierarchical process modelling and execution approach is presented in this paper. This approach supports stepwise elaboration of incompletely-specified processes on-the-fly. Further elaboration of a process is innovatively modelled as essential steps towards the process goal, thus being scheduled to execute as ordinary tasks. © Springer-Verlag Berlin Heidelberg 2005.