User's guide chapter 3 section 11 & 12

Previous: Chapter 2 Next: Chapter 4

3.11 – Action Logic

ProcessModel allows you to design custom behavior in your model by using action logic in which you enter simple but powerful logic statements. Action logic allows you to define special logic that may not be easily defined using the normal property fields. Examples would include assigning values to attributes and variables or performing a test using an IF…THEN statement.

Action logic can be defined for any activity, storage, arrival or routing by clicking on the Action tab of the properties dialog.

Depending on the object or connection for which the action is defined, only certain statements and other logic elements are meaningful and therefore valid. The valid statements and logic elements (variables, attributes, resources, distributions, operators, and scenario parameters) are available via the Keywords and Filters (Keywords & filters) dialog. These statements and elements may be pasted from the list box into the action window to help you construct the desired action logic.

Action Logic zoom window

You may also start typing your saved attributes, variable, scenarios, scenario parameters, activity, entity, resource names or any of the ProcessModel supported statements, functions or distributions to see a help menu popup to help you easily populate what you wish to add.

Auto help for action logic

Paste elements into the action window

1. Click the Keywords and Filters Keywords & filters button on the action logic window.

2. Select the type of element (including statements) you want from the pull down box.

3. Select the specific element or statement from the list box.

4. Press the Insert button to insert the element at the position of the cursor in the action edit window or simply double-click the item.

Important information to be aware of Action Logic often uses expressions (combinations of attributes, variables, numbers, and operators) in assigning values to attributes or variables, testing the value or state of a variable or attribute, etc. For more information on expressions and valid operators, see Expressions.

See Also To learn advance functions / Keyboard shortcuts, see “Advanced Options for Action Logic Window”.

3.11.1 – Functions

Functions provide you with critical system information at any given time during the simulation. They can be used in an assignment statement to set the value of a variable or attribute or in an IF…THEN statement to make a decision based on system information. There are several system functions: Clock(), Contents(), FreeCap(), FreeUnits(), GroupQty(), OwnedResource(), Percent(), and ResQty().

 System reserved words cannot be used as variable names, attributes, or scenario parameters.

Clock( )



CLOCK( ) or CLOCK(time unit)


a_Time = Clock( )
v_Time_in_System =
Clock( ) – CycleStart
If Clock(Hr) > 24

The default clock function returns the elapsed time of the simulation clock in minutes. It can be accessed, but not assigned a value. For example a variable could be assigned the value of the clock in minutes: v_Var1 = Clock() would result in the number of minutes elapsed in the simulation assigned to the variable. To assign the number of hours that have elapsed, use v_Var1 = Clock(hr), and to get the number of seconds, use v_Var1 = Clock(sec).

More Information

A common use of the Clock( ) function is collect and plot individual cycle times for entities. It can be used to help collect individual times in just part of the model or individual entities for the entire cycle time. Why would this be important? Doesn’t ProcessModel automatically collect and report the average cycle time for each entity type? Yes it does, but a major reason for simulation is to dig deeper than averages, because averages are misleading.

ProcessModel automatically notes the simulation clock time when each entity first enters the process and writes that information to a default entity attribute called CycleStart. You can use a formula below calculate and record the processing time for each entity.

Example: v_Time = Clock() – CycleStart

Each entity that crosses the action statement that contains this formula will find out the current simulation time, subtract the starting time of the entity and write the result to variable defined (in this case, v_Time).

Many times, however, it is helpful to know the time it takes for an entity to complete only a portion of the process, for example activities 4 to 6 of a larger process. In this case, you would enter a_attribute1 = clock() in the action logic of the route entering activity 4. [Not specifying a unit of time by not putting anything in the parentheses after “clock” causes ProcessModel to use the default time unit which is minutes.] This would cause ProcessModel to note the time that each entity enters activity 4. You would also enter v_variable1 = clock() – a_attribute1 in the action logic of the route leaving activity 6. This would cause ProcessModel to take a new clock reading, subtract from it the first clock reading, and write to a variable that reflected the difference which you could then track in your output reports.

Important information to be aware of If you change the default time units to hours, then the value returned will be divided by 60. If you change the default time units to seconds, then the value returned will be multiplied by 60.

Contents(name of activity) 

Returns the total number of entities at an activity. Use CONTENTS() to make decisions based on how busy an activity is. Using CONTENTS() to keep track of the number of entities at an activity requires fewer steps and allows more flexibility than using variables to count the number of entities that enter and exit an activity. For example, the second syntax does in one statement what would require several statements without the CONTENTS() function.


A car wash has an activity called Wash that often gets too busy for one operator to handle so the supervisor then comes to help. The logic below models this situation with an IF…THEN statement and the CONTENTS() function. As long as the activity contains fewer than three cars, the worker processes any arriving car. However, if the contents of the activity are greater than three, the Supervisor may also be used.


GET Worker


GET Worker OR Supervisor


FreeCap(name of activity) 

Returns the available capacity of an activity (an integer).


Suppose an entity can be routed to one of two identical ovens for a curing process. However, you would like to ensure the ovens are loaded as evenly as possible at all times. The following logic could be used to set an attribute (called a_Router) to a 1 or a 2 based on the available capacity of the ovens. Conditional routings would then be used to route to the appropriate oven:



ELSE {a_Router=2}

FreeUnits(name of activity or resource) 

Returns the free units of an activity or resource (an integer).


The example below demonstrates the use of the FREEUNITS() function to adjust the processing time for an entity based on the number of units of a resource available to process it. Once a Plane arrives at a passenger gate, it captures a certain number of resources named BH (Baggage Handlers). Operation logic at the gate determines how many BH resources have been captured and, accordingly, how long it will take to service the Plane. The more Baggage Handlers a Plane captures, the less time it takes to service it.


DO TIME(2 min)




GroupQty( ) 

Returns the number of entities in a batched or loaded entity (a loaded entity is an entity with other entities attached to it). If the entity is a loaded entity, it will return only the number of loaded entities, not the base entity. For example, if you attach four Castings to a Pallet, the GroupQty() will return the number of Castings (i.e. 4), which does not include the entity Pallet.

In the case of multiple levels of groups and loads, GroupQty() returns the number of entities in the uppermost level only.


A group of documents called Folder arrives at the Secretary in-box and is processed for some amount of time according to the number of documents in the folder. Each document takes 3.0 minutes to process.

TIME (GROUPQTY() *3.0 min)


Returns the n th resource currently being used by the entity. Each resource is referenced according to the order it was put into use so that the longest held resource is OwnedResource(1). The most recently captured resource can be referenced by omitting the number: OwnedResource().


The OwnedResource() function is useful when a decision must be made based on the resource that was captured. For example, suppose an entity captures either Worker_1 or Worker_2 in order to perform an activity. If Worker_1 is used, the activity takes 5 minutes. If Worker_2 is used, the activity takes 6.5 minutes. This can be defined using the following Action logic.

GET Worker_1 OR Worker_2
IF OWNEDRESOURCE() = Worker_1 THEN {TIME(5.0 min)}
ELSE {TIME(6.5 min)}

Important information to be aware of This function cannot be assigned a resource name in Action logic. For example, an assignment statement like OwnedResource() = Worker_1 will generate an error.


The percent function allows you to execute one or more statements only a certain percentage of the time. Used in an IF…THEN statement, the function returns a TRUE or FALSE.

To use the percent function, enter PERCENT(n) where n is the percentage of the time that the statement will return a TRUE condition in an IF…THEN statement.


In the first example, logic following the THEN statement is executed 21.5% of the time. In the second, logic following the THEN statement is executed 35% of the time and the logic following the ELSE statement is executed 65% of the time.



ResQty(name of resource) 

Returns the number of units of a specific resource that the current entity owns. You can use RESQTY() to determine the amount of time necessary to process an entity based on the number of units of a resource the entity owns.


The example below demonstrates the use of RESQTY() to adjust the processing time for an entity based on the number of resources available to process it. Once a Plane arrives at a passenger gate, it captures a certain number of resources named BH (Baggage Handlers). Operation logic at the gate determines how many BH resources have been captured and, accordingly, how long it will take to service the Plane. The more Baggage Handlers a Plane captures, the less time it takes to service it.




3.11.2 Statements

Statements are simply commands to be executed at particular stages in an entity’s progress through the process. The following pages explain in detail each statement listed below.

 System reserved words cannot be used as variable names, attributes, or scenario parameters.

( ) = ( ) assignment


Comments You can add explanatory comments to your action logic by placing special characters in front of the comment. Comment lines are for user information only and the simulation ignores them during run time. To include a single-line comment, use a pound sign “#” or two forward slashes “//” at the beginning of the line. Multiline comments begin with a “/*”… and end with a “*/”. Some statements and functions such as GET or FREE are not ignored when found in a single comment line. To ensure they are ignored, you must use the multiline /* . . . */ comment indicators, and the ending “*/” must appear on a different line than the opening “/*”.

 FREE, GET, and JOINTLYGET, PERCENT and GROUP statements are not ignored by the // comment indicator. Use the /* … */ comment indicators. These indicators are normally used to comment multiple lines. So if you are only commenting out a single line, the closing */ must appear on a second line since it cannot exist on the same line as the opening /*.

For example:

IF Test = Reject THEN INC RejectQty
/*Number of rejects increased
for each test reject.*/


// The logic below describes how rejects are handled.

( ) = ( )

This is the assignment statement which allows you to assign a value (or descriptor) to a variable or to one of the attributes defined for your entities.


assignee = assignor

assignee The variable or attribute to which the value is assigned.
assignor The value assigned to the variable. This could be another variable or attribute, a pre-defined descriptor, or a mathematical expression.


In the first example, the attribute a_ Attr1 is assigned a value of 2. The second example assigns the value of a_ PO_No to the attribute a_ Invoice_No . Number three assigns the descriptor Red to the attribute a_ Color . And the last example assigns the product of 5 and the value of Base to the attribute a_ Size.

1) a_Attr1 = 2
2) a_Invoice_No = a_PO_No
3) a_Color = Red
4) a_Size = 5 * Base


The ANIMATE statement allows the control of the animation speed through the action logic dialog.



speed A numeric value between 0 and 100. One is the slowest and one hundred is the fastest speed of animation. A speed of zero turns the animation off.


In the first example, ANIMATE statement is used to turn the animation off so that the model will run ahead in time quickly. In the second example the speed of animation is set very slow (usually to show a particular entity or activity). In the third example the speed of animation is set to the highest possible speed with animation still on (often used to help the user gain a “feel” for the general flow and buildups that would occur over time.

1) animate(0)
2) animate(10)
3) animate(100)

The ANIMATE statement is usually implemented by placing a separate entity, arrival and activity combination in the existing model. Scheduled arrivals work well because the exact time can be assigned for the arrival(s) and individual action logic applies for each scheduled arrival. The first arrival could be used to “fast forward” to a time in the model of particular importance, while the next arrival could be used to slow the animation for inspection of a particular aspect of the simulation and then a third to again “fast forward” to see the results.


The decrement statement allows you to decrement a variable or attribute’s value. It subtracts one (the default) or more from the value of the variable or attribute.


DEC name [, expression]

name This is the name of the variable or attribute to be decremented.

[expression] You can optionally decrement the variable or attribute by more than one using an expression which can be a constant or a mathematical expression. The name and expression must be separated by a comma. (The square brackets illustrate only that this element is optional.)


The following are several easy-to-understand examples. The first decrements the value of v_ Var1 by one. The second decrements the value of a_ Attr1 by five. The third decrements the value of Number_in_System by the value of an attribute called a_ Batch_Size.

1) DEC v_Var1
2) DEC a_Attr1, 5
3) DEC Number_in_System, a_Batch_Size


Pauses the simulation and displays a message. The simulation will resume when the user selects OK.


DISPLAY “< text string >” [,< attribute / variable / function call >]
DISPLAY “Now completing the 100th set”
DISPLAY “The current number of entries is: “, Var1
DISPLAY “Var1 = “, Var1 $ CHAR(13) $ “Attr1 = ” $ Attr1

text string The message ProcessModel will display. The text string must be enclosed in quotes.

[attribute / variable / function call] The text string or numeric value you wish to display.

After the original set of information (i.e. text string, variable) the “$” character is used to add additional information (i.e another text string or variable). You can force a carriage return by using the statement CHAR(13). Each new item that is appended to the statement must be prefaced with the “$” character.

Example 1

This example displays a message whenever a new order type begins processing at the current activity. A variable, v_ Last_Order , stores the order type of the last entity processed at the activity. If the current entity’s a_ Order_Type attribute value is different from the previous order type, ProcessModel displays a message stating the new order’s type.

IF Order_Type <> Last_Order THEN

DISPLAY “New Order Type: ”, a_Order_Type
v_Last_Order = a_Order_Type


Example 2

This example displays the entity name during simulation.

Display “Entity Name = “, Name


Display “Entity Name = “, Ent(Name)

Using just Name will display the entity number rather than the text name. Name is the system defined attribute which contains the numeric value of the entity name. Ent(Name) will display the text name of the entity.

Important information to be aware of The display statement is valuable for debugging complex models and for halting a model temporarily during a presentation to display information.


The free statement allows you to free a resource (or resources) being used by the current entity.


FREE [ quantity ] resource
FREE [ quantity ] resource , [ quantity ] resource , …

[quantity] The number of units of the following resource to free. If no quantity is used, the quantity is assumed to be one. (The square brackets illustrate only that this element is optional.)

resource The name of the resource or list of resource names to be freed. If any resource specified is not being used by the current entity, it is simply ignored.

ALL The keyword used with the FREE statement to free all captured resources.


In the following example, an entity, which earlier captured the resource Operator, frees the Operator after a three minute activity time. This action is followed by an increment of the variable called v_TimesUsed.

TIME(3 min)
FREE Operator
INC v_TimesUsed

If no action statements follow the freeing of a resource, the resource can just as easily be freed by drawing a Free resource assignment connection between the resource and the activity.


The get statement enables an entity to obtain a resource. ProcessModel attempts to capture the resources in the order they are listed. If multiple resources are requested, but not available, those that are available will be captured and tied up until all are available.

If you get and free your resources in action logic (rather than with a connector line), the entity must enter the activity before it knows whether a resource is available or not. Therefore, if the resource is not available and the entity must wait “in” the activity for the resource to be available as compared to the GET/FREE route where the entity will wait at the input queue for the resource to be available before entering the activity.

To have the GET/ FREE action logic to behave in the same manner as the GET / FREE routes, add an extra activity that will server as the input queue, before the the activity where you want the resource to work. Remove the input/output queue from the new activity as well as the working activity. Change the capacity of the new activity to the input queu size for the work activity and GET the resource at the new activity.