Page 151 - ExtendSim User Guide
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Items, Properties, and Values 125
Item properties
• Ifthestartconnectorisnotconnected,theschedule'sitemcreationtimesaresynchronized with the simulation run's absolute time. For example, if the schedule's first create time is at time 2 and the simulation's start time begins at time 0, an item would be created when simu- lation time reaches 2. However, if the starting time entered in the Simulation Setup dialog is 4, the item scheduled at time 2 is never created.
• Ifthestartconnectorisconnected,suchastoaDecisionblock(Valuelibrary),theschedule's item creation times are relative to when the connector is activated. For instance, assume sim- ulation starting time is 0 and the first item is scheduled for creation at time 11. If the start connector gets activated at simulation time 5, then the first item will be created at time 16 (5 plus 11).
☞ Starts are activated whenever the connector receives a message with a True value (defined as greater than or equal to 0.5).
The Create block’s Options tab provides choices for how the start connector should behave, as discussed below:
• Followsschedule.Thisisthedefaultoptionandshouldbeusedformostsituations.Once the start connector is activated, the entire schedule will be executed. Any new activation sig- nals arriving before the current schedule has completed are ignored.
• Generatesoneitempermessage.Thisisanadvancedchoiceforspecialsituations.Itis most often used when a custom-created block is connected to the start connector and you want an item to be instantaneously generated for every message. With this choice, the sched- ule is restricted to one row. Each time the start connector is activated, the row is executed.
• Generatesoneitemperevent.Thisisanadvancedoptionforspecialsituations.Withthis choice, the schedule is restricted to one row. Each time the start connector is activated, a zero-time event is scheduled. Once the Create block gets the zero-time event message, it will execute the schedule.
Item properties
A property is a quality or characteristic that stays with an item as it moves through the model. Some properties can be assigned to items by the model builder; others are automatically assigned by the system.
An item’s properties include:
• User-assignedattributes.Thesearediscussedinthenextsection.
• Priority. See page 133.
• Quantity. See page 134.
• System-assigned attributes. See page 137.
Item attributes
Because they allow items to be distinguished from each other, item attributes play a very important role in a discrete event simulation. They are especially useful for telling an activity- type block how long the item should be processed, or for determining where the item should be routed before or after processing. The following sections describe how to create, use, and man- age attributes.
Discrete Event

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