Rockwell Automation Arena Users Guide - Manual (Page 21)

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Review application (Process module)
Remember that as we create the flowchart, we’re looking at the process from the perspec-
tive of the entity. The Create module is a starting point for an entity’s flow through the
system being modeled. Next, in our case, the application will be reviewed for complete-
ness by a Mortgage Review Clerk. Because this will take some amount of time, holding
the entity at this point in the flowchart for a delay and requiring a resource to perform the
activity, we use a Process module. We’ll call this process Review Application.
For the time delay, we also want to capture the natural variability that exists in most
processes. Very often, for work done by people or equipment, a triangular distribution
provides a good approximation. You specify the minimum time in which the work could
be done, the most likely value for the time delay, and the maximum duration of the process.
During the simulation run, each time an entity enters the process, Arena will calculate a
sample from the distribution information you’ve provided—in our case, a triangular
distribution. Over the course of a long simulation run where thousands of individual
samples are taken, the times will follow the profile illustrated next.
What are entities?
Entities are the items—customers, documents, parts—that are being served, produced,
or otherwise acted on by your process. In business processes, they often are documents
or electronic records (checks, contracts, applications, purchase orders). In service
systems, entities usually are people (the customers being served in a restaurant, hospital,
airport, etc.). Manufacturing models typically have some kind of part running through the
process, whether it’s raw material, a subcomponent, or finished product. Other models
might have different types of entities, such as data packets in network analysis or letters
and boxes in package-handling facilities.
You may have different types of entities in the same model. For example, customers
moving through a check-in counter at an airport might be separated into regular, first-
class, and priority entity types. In some cases, entity types might be of an altogether
different form rather than classifications of some basic type. For instance, in a pharmacy,
prescriptions would be modeled as entities, running through the process of being filled. At
the same time, customers might be competing for the pharmacist’s attention with medical
inquiries; they would also be modeled as entities.
Appendix A
describes the
distributions
available in Arena.