Written by on Friday May 3rd 2013 in SIMUL8 Tips, Technical Corner

SIMUL8 Tip – SIMUL8 2013’s State Charts

What is a ‘Work Item State’?
This is a completely new way to look at work items as they travel through your simulation. As Work Items move through a process you can associate them with states, or conditions.  These do not necessarily relate to their physical position in the simulation,  and states can be used to define behavior. For instance Patients can be unwell, in treatment, or well while all under the care of the same outpatient clinic.

Simulations are normally built using Simulation Objects (Start Points, Activities, Queues etc.) and for most simulations you can keep things quick and simple using those objects.  However, occasionally, you need an additional way to describe what happens to work items. This is where Work Item State Charts take over and allow the description of your process without having to create a series of awkward “Logical Activities”.  Work Item State Charts work independently from, or in unison with, the normal Simulation Object work item flow.

An Example:


A patient enters a hospital for a routine operation and during their stay they go though a series of stages, this is all simulated with traditional SIMUL8 Simulation Objects, but while they are in hospital there is a chance they will acquire an infection not related to their original reason for the hospital visit.

A Work Item State Chart can be used to describe and simulate the “Hospital Acquire Infection” process in parallel with the normal process:

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Work item States are stored in SIMUL8 Labels. All the states shown above are stored as labels on the work items. Each label has the values 0 or 1 (shown in the Label Viewer as “No” or “Yes”). The only value a state label can have is 0 or 1.  Transitions (shown as arrows) describe how and when work items transition between states.

Create a Work Item State Chart by drawing it on the screen (drag a new state from the Work Item State Chart palette onto a simulation window. Draw arrows (transitions) between states in the same way that you draw routing arrows between Simulation Object.

If a state is drawn inside another state (for example “Not Diagnosed” is drawn above inside “Infected”) then any work item entering the enclosed state (Not Diagnosed) will automatically enter the enclosing state (Infected).

Transitions can sometimes be easier to describe by inserting a “Transition Decision” that can branch a work item change of state in a number of different directions:
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Why would I use them?
Discrete Event Simulation offers you the ability to make decisions based on how items flow through your process. With State Charts you can make decisions based on the status of an item at any stage of a simulation run.

In strategic healthcare planning, you can see the ‘state’ of all individuals in your population at a glance, and make capacity and pathway decisions. You can trigger events based on a person’s state – so if they become well, they can leave hospital.

Whatever your industry, the applications of this powerful new feature are endless. This will not only simplify many of the simulations you create, they remove the need for Visual Logic to control labels. It will also open so many potential areas that you can now simulate.

For more information on the State Chart features, visit our how to guide.