An Introduction to Simio® for Arena Users

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In a moment we will discuss process modeling in Simio. At that time we will introduce the concept of a "dumb" token that carries information and executes a process. An Arena entity corresponds to a token in Simio.

Simio Resources

Both Arena and Simio have the concept of resources. However in Simio the concept is quite different and much more robust. Any object in Simio can seize and release any other object. For example a Server object could seize and release a Worker object. However a seize operation requires a negotiation between the objects involved. In the above example the Worker object could refuse the seize request because he/she has other activities to perform. Hence in Simio objects allow or disallow themselves to be seized and released by other objects.

The Role of Processes in Simio

As an Arena user you have built your models using a process orientation. In Simio the process orientation still exists, however its role within model building is completely changed. In Simio the process orientation is used to either customize the behavior of an existing object, or to create new object definitions.

A process in Simio is very similar to a process in Arena, with slightly different terminology. A process in Simio is comprised of steps, elements, and tokens. Tokens flow through a process executing steps that alter the state of one or more elements. Hence steps are like Arena blocks, and tokens are like Arena entities.

You can build many simple models in Simio by relying totally upon the object definitions from the Standard Library. However once you start modeling complex real-world examples, you will likely encounter the need to use your Arena-like process modeling skills to extend the behavior of these objects. This is one of the primary roles of process modeling in Simio.

When you place an object from the Standard Library into your facility model, you can have the object run "add-on" processes at specific points in the logic. An "add-on" process is simply a logical process that you have created to perform some specific action such as assigning a state variable, seizing a resource, referencing information in a table, etc. For example the Source object has four "add-on" processes: Initialized, Creating Entities, Created Entity, and Exited. You can add your own custom logic to this object at any of these four points in the object logic.

The second major role for process modeling in Simio is for creating new object definitions. An object definition is simply a model for how instances of that object should behave. These models can be built in three primary ways. The first is to build facility model using one or more existing object definitions;

i.e. traditional hierarchical modeling. For example you might combine two servers in series into a new object definition representing tandem servers. The second way is to define the object using a set of processes. Objects built in this way are referred to as base objects. This is the most flexible and powerful approach and is the method used for creating the object definitions in the Standard Library. The third way is referred to as sub-classing. In this case you inherit the behavior of an existing object and then modify it by overriding or adding one or more processes. Once you successfully make the transition from a process modeling perspective to an object modeling perspective your Arena-like process modeling skills will be very useful for both enhancing the use of the Standard Library objects, and also creating new object definition libraries for use in your modeling activities.


As an Arena user switching to Simio you will be faced with the challenge of changing your modeling perspective to an object-based approach. Model your system from the perspective of the "things" that make up the system, and not the logical process flows within your system. Employ your process modeling skills for the purpose of customizing the logic for an existing object (i.e. add-on processes), or for building libraries of new object definitions for use in your models. Once you have mastered this new approach you will be able to fully exploit the power of Simio.

About The Author

Simio® LLC was founded by Dennis Pegden, Ph.D. to reinvigorate the field of simulation modeling. A 33year veteran of the simulation industry, Pegden's career highlights include leading the development of SLAM (marketed by Pritsker and Associates) and founding Systems Modeling Corporation, now part of Rockwell Automation. Pegden also led the creation of the simulation products SIMAN and Arena. Simio's management team brings one hundred five years of combined experience in the simulation market. Contact Dennis Pegden at To evaluate Simio, click here.

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