To foster modularity as well as design knowledge encapsulation and reuse, and to reflect the subdivision of industrial process flows in process modules, process submodules, process steps, and operations, the process flow representation supports hierarchical and parameterized process modules that allow the definition of large process flows in terms of predefined blocks (Figure 5.4).
Figure 5.4:
Hierarchical process flow representation.
A recipe consists of a sequence of operations and corresponds to
a step in a process module. Process modules are combined to form a
process flow.
Modules contain any number of subordinate modules and process steps. They are either inserted into the process flow description or referenced by symbolic names, the former option ensuring a compact capture of the process flow for convenient data exchange with remote sites, the latter supports sharing of externally stored process module libraries by various users.
A module allows local symbols to be defined that can be used as parameters for all steps and sub-modules belonging to the module. Moreover, step output data can be assigned to local symbols and thus be passed to other steps or upstream in the flow hierarchy.