The(71) is a general description of the architecture of a workflow management system used by the WFMC, in which the main components and the associated interfaces are summarized. The workflow enactment service is the heart of a workflow system which consists of several(72). In a workflow system, a process is specified using the process definition tool. Usually, processes are defined in terms of a(73), which consists of(74) indicated using a circle, and(75) shown as a rectangle. These two components can be linked by means of a directed arc.

A．waterfall model

B．workflow reference model

C．evolutionary model

D．spiral model