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About Zones   

This topic will introduce you to the basic concepts of the Zone, which is one of the shared asset objects. After reading this section, you should have a basic idea of what a Zone is and when you might need one. Zones represent a fairly abstract concept and so the next two sections provide analogies for understanding. The final section discusses use cases for the Zone asset.

This topic contains the following sections:

Purpose of the Zone

You can use a Zone for two reasons:

  1. To collect statistics across multiple activities
  2. To then use those statistics to restrict access to those activities

A real-world example of uses for the Zone might help to explain these two functions. Imagine that you wanted to use the process flow module to simulate a self-serve copy center. Perhaps you have a group of color-copy machines and a group of black-and-white copy machines. Customers who come to the copy center might want to make either color copies or black-and-white copies. However, there is a limit to how many machines can be in use at the same time. When either the color-copy or black-and-white machines are all in use, the Zone can restrict access to the machines. In other words, the customers will have to wait in line until the kind of machine they need becomes available. Using a Zone makes it possible to simulate this kind of behavior. You could possibly create one Zone for the color-copy machines and another for the black-and-white machines.

Imagine also that you want to collect data about things such as:

  • The average number of color or black-and-white copy machines that are used in a given period of time
  • The average wait time for customers who are waiting to use either color or black-and-white copy machines
  • The average amount of time it takes for customers to complete their copies

Zones are capable of collecting this kind of statistical data as well.

The following two sections will explain how each of these two functions (collecting statistics and restricting access) will work in an actual process flow.

Collecting Statistics

A Zone can be used to collect statistics for an area of your process flow. For example, suppose you made the process flow shown in the following image:

Suppose that you want to know statistics about just the left portion of the process flow, as shown in the following image:

Specifically, say you wanted to know the answer to the following questions:

  • What is the maximum content of the left side?
  • What is the average content of the left side?
  • How long, on average, does it take tokens to get through the left side?

A Zone can be used to answer these questions. In order to create the statistical boundary shown in the preceding image, you would add an Enter Zone activity and an Exit Zone activity, along with a Zone, as shown in the following image:

The Zone will automatically record the input, output, content and staytime for all tokens that enter and exit the Zone. The following image shows the process flow during a simulation run, with many activities in the Zone.

The next image shows the Zone's Statistics Window, with the maximum content, average content and the average staytime highlighted.

Restricting Access

Zones can be used to restrict access to a set of activities. For example, a Zone might represent a warehouse or a shipping container, and tokens might represent items. Any token that enters the Zone would take up space or weight (or both) within the Zone. Usually, there is some limit on space or weight. The Zone can be used to enforce those limits.

The simplest way to restrict access to a Zone is to limit the number of tokens allowed in the Zone. Using our previous example, suppose at most 7 tokens (which represent items) can fit in the Zone. The Zone has a Use Max Content option, shown in the following image, that enforces that rule:

The following image shows a snapshot during execution, with the max content set to 7:

Notice that there are three tokens on the Enter Zone activity waiting to be allowed into the Zone, which currently has 7 tokens in it. Each token must wait for room to free up in the Zone before entering.

Zone Subsets

You can also use a Zone to gather statistics about a particular subset of tokens. For example, you might be interested in knowing the number of tokens that have an itemtype label value of 1, or the number of tokens that have a weight label value greater than 250. You can collect these statistics by creating a Zone Subset.

You can restrict access to a Zone based on Zone Subset statistics as well. It is possible to restrict the number of tokens within a subset, or a total quantity of label values (like the total of all weight labels). A token will not enter a Zone until it complies with all subset restrictions.

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paul.t contributed to this article


FlexSim 2016.1