When building models the general rule
you should follow is: one generic process
per flow. As with any rule, this one has its exceptions. When different processes
interact with one another to produce a flow, you may want to "blend" the processes
together to generate the flow.
The above figure shows the most
commonly-encountered blend of generic
processes: the ordering process. In the diagram, the flow of orders is a blend of two
Stock-Adjustment processes and one Co-Flow process. The Co-Flow process
ensures that orders will be sufficient to cover shipments. The growth factor ensures
that orders will account for anticipated trends in shipments. The Stock-Adjustment
processes ensure that Inventory and Backlog will seek their goals. Investment ~ in
which capital equipment is acquired to meet both retirement and to expand
capacity - and hiring — where people are brought on to replace turnover and to
correct labor shortages — are two other examples of the ordering process.
The behavior of the ordering process depends
on the specifics of the processes
that are being blended together to produce the flow. As such, the ordering process
has no one characteristic behavior pattern.
In general, adhere to the "one generic
process per flow" rule. Only when different
generic processes combine with one another to produce a flow should you use a
blend of processes.
Fig
