In hierarchical system design, refinement allows to incrementally increase the level of detail in the system description. Several notions of refinement have been investigated in process theory and in object-orientation. From a process algebraic viewpoint, an object as the basic unit of structure and control can be understood as a process. Then \em action reification - the replacement of actions by transactions in object-oriented specification - corresponds to \em action refinement in process algebra where actions are replaced by process terms.