NumberHolder Components

Building a Model with Elementary Components

NumberHolder Components

There are various ways to both save information and retrieve information from holders. The values of attributes carried by transactions can be saved in a holder when the transaction enters the holder. Alternatively, a value can be saved in a holder when a transaction enters a trigger in some other part of the simulation model. For example, suppose that you want to save the value of a transaction attribute called "weight" in a NumberHolder.

Figure 2.12: Number Holder Saving "weight" Attribute

In the model fragment in Figure 2.12, when the transaction arrives at the Trigger, the value of the weight attribute in that transaction is saved in the NumberHolder. Now, another part of the simulation can query the NumberHolder to find the current value of weight. You could also route the transaction directly to the NumberHolder and update its state that way.

You specify the name of the attribute that is stored in the NumberHolder in the NumberHolder Control Panel, which is displayed by selecting Control Panel... selection on the pop-up menu on the NumberHolder.

Figure 2.13: Number Holder Control Panel

Notice that the NumberHolder control panel shown in Figure 2.13 has the attribute name "weight" in the Attribute Name field.

The transaction sets the NumberHolder when it arrives at the Trigger because the Trigger Control Panel, as shown in Figure 2.14, has the NumberHolder component selected and the setFromAttribute selected.

Figure 2.14: A Trigger Control Panel

The Initial Value field in the holder control panels provide a way of initializing the holder. This is useful when using the holder as a counter of resources. When the NumberHolder decrements, there is one less available resource. Other parts of the model may query the holder to see if there are resources available for certain activities. In this case it may be desirable to have an initial pool available.

The Disable Reset check box will disable the resetting of the last value in the holder when the simulation reset button is pressed. If not checked, when the reset button is pressed the holder is reset to its initial value. If checked, the reset button has no affect on the holder.

The following documents the logic of the NumberHolder component:

Transaction Arrival

sets the value as specified in the NumberHolder Control Panel; then flows the transaction to each arc directed away from the component.

Request for Transaction

passes on the request to all arcs directed into the component.

Are You Busy Message

if any component on an arc leading out of the Trigger is busy, then return TRUE; otherwise, return FALSE.

Query Message

Keyword	Meaning
currentValue	returns the value in the holder at the current time
id	returns the component's unique identifier.
value	returns the value in the holder when the transaction passed through it.

Trigger Message

Keyword	Meaning
+	adds the transaction attribute to the value.
-	subtracts the transaction attribute from the value.
clearSetFromAttribute	clears the value then sets it.
controls	displays the Holder Control Panel.
decrement	decrements the value.
increment	increments the value.
print	prints the value on the SAS Log window.
reset	resets the value and the value.
setFromAttribute	sets the value from the transaction attribute.
setFromTrigger	sets the value that is assigned with the
	Trigger Value button in the Trigger Control Panel.
setTimenow	sets the simulation time into the value.
start	starts the holder.
stop	stops the holder.

Chapter Contents
Previous
Next
Top