This paper addresses a methodology for developing the various user interfaces (UI) of a workflow information system (WIS), which are advocated to automate business processes, following a model-centric approach based on the requirements and processes of the organization. The methodology applies to: 1) integrate human and machines based activities, in particular those involving interaction with IT applications and tools, 2) to identify how tasks are structured, who perform them, what their relative order is, how they are offered or assigned, and how tasks are being tracked. For this purpose, workflow is recursively decomposed into processes which are in turn decomposed into tasks. Each task gives rise to a task model whose structure, ordering, and connection with the domain model allows the automated generation of corresponding UIs in a transformational approach.