Page 340 - ExtendSim User Guide
P. 340

Tips and Techniques
Item library blocks
• AtableintheFlowAttributestabisusedtoenteradescriptivetextlabel(string)for each potential attribute value for a selected string layer attribute. For more information, see “Flow attributes” on page 353.
• OthertablesintheFlowAttributestaballowyoutoselectaflowlayerattributefor renaming or deleting, and display blocks that use the selected attribute.
• Manageflowunitsandselectglobalandadvancedoptionsfordiscreteratemodels.Formore information, see “Global and advanced options in the Executive” on page 436.
• SetinformationfortheLPsolverusedindiscreteratemodels.Formoreinformation,see “LP technology” on page 448.
☞ Unless you use string attributes, it is rare that you would need to make any changes in the Executive’s dialog. Most of its options are for advanced users.
The Item Templates library contains templatessubmodels within hierarchical blocks for common modeling situations such as emptying a queue at intervals or selecting the shortest queue.
Block types
As discussed on “Item connector messages” on page 321, Item library blocks pass messages through item connectors. There are three types of item-based blocks that determine how the item connector messages are handled:
• Residence-typeblocksareabletocontainorholditemsforsomedurationofsimulation time. Some residence blocks post events and some do not.
• Passing-typeblockspassitemthroughwithoutholdingthemforanylengthofsimulation time. These blocks implement modeling operations that are not time-based; they usually do not post future events.
• Decision-typeblocksroutetheitemsthroughthemodel.Theseblockschoosearoutebased on an item property, a random value, a sequence, or an input from a connector. Depending on what options are selected in the block, a decision-type block may or may not be able to hold onto items.
Why block types matter
Knowing these categories of blocks and how they relate to the processing of items will help you to build better models. For example an item will not enter a passing block before it has been determined that there is space in the next downstream residence block. And when you debug models it is useful to understand where the items can reside for any amount of time, as well as the time required for an item to move from one residence block in the model to another. In addition, some of the options in the blocks refer to specific block types. An example of this is the Transport block where you can specify that the distance to the next block is from the Transport block to the next non-passing (residence or decision) type block.
Discrete Event

   338   339   340   341   342