2008 Winton. Modeling Resources

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Esther Lloyd
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1 1 Modeling Resources

2 2 Model Entities System entities may utilize a "pool" of resources Examples The tables in a cafeteria Shopping carts in a store Rental cars Representing a pool of resources Use a number that is decreased whenever an entity receives a resource and is increased whenever an entity releases a resource The members of the pool are treated as entities in their own right They have attributes that need to be modeled (e.g., a rental car's mileage).

introduce items into the model Does not "push" items (unlike a Generator Block) Items have to be pulled as in the (non-sensical) example All items in the Resource block are

3 3 Resource Block The Resource Block (Discrete Event.lix) provides a pool of items The number of items is set in the block's dialogue Can be dynamically adjusted by the value of an item input to the change connector Can be used to introduce items into the model Does not "push" items (unlike a Generator Block) Items have to be pulled as in the (non-sensical) example All items in the Resource block are immediately pulled by the Exit block The more normal expectation is that an item created by a Generator Block (e.g., a customer) takes a resource from the pool (e.g., a basket of golf balls), does something representing use of the item (e.g., using the practice tee), then returns the resource to the pool and exits.

4 Joining an Item With a Resource Basic model structure input item X Batch Block (Discrete Event.lix) (combines an item from input with one from the resource pool) Unbatch Block (Discrete Event.

4 4 Joining an Item With a Resource Basic model structure input item X Batch Block (Discrete Event.lix) (combines an item from input with one from the resource pool) Unbatch Block (Discrete Event.lix) (separates the input item from the resource item) input item exits resource item standard queue/server setup Resource Block (Discrete Event.lix) resource item returns to pool If the Batch block has been able to pull an item from the Resource block, then the Resource Available value at the select connector will be 1 and the input item will be pulled into the Batch block to be combined with the resource item Otherwise, the item will exit at X Once past the activity part of the model, the combined item from the Batch block is separated by the Unbatch block, with the input item passing on and the resource item returned to the pool

5 5 Resource Pool Blocks The Resource Pool block (Discrete Event.lix) provides a named pool that corresponds to modeling a pool of resources with a number rather than a set of items The Queue, Resource Pool block (Discrete Event.lix) allocates resources from a named pool when they become available, and queuing the item otherwise The Release Resource Pool block (Discrete Event.lix) releases resources back to a named pool when an item passes through

6 6 Resource Pool Block The Pool is named and a value established via its dialogue Controls assignment of items via the Queue, Resource Pool block FIFO By priority Items can be allocated (as a number) to an attribute

7 7 Queue, Resource Pool Block The name of the pool it draws from is entered in its dialogue It only holds an item on queue if there are not enough resources in the pool If the maximum queue length is set to 1, items are rejected once the pool runs out of resources Resources can be assigned to an attribute When enough items are available for an allocation, the Resource Pool determines the order in which it allocates resources to items on queue according to criteria established in the dialogue of the Resource Pool Block

8 8 Release Resource Pool Block Returns resources to the Resource Pool when an item passes through Number of available resources is incremented An item can release resources it did not acquire Resources can be released via an attribute

9 Typical Model Use Items enter a model, acquire a resource, perform some activity, then return the resource and leave Item in Resource Pool Block (Discrete Event.

9 9 Typical Model Use Items enter a model, acquire a resource, perform some activity, then return the resource and leave Item in Resource Pool Block (Discrete Event.lix) (name is "PoolName") Release Resource Pool Block (Discrete Event.lix) (pointed at "PoolName") Item out Queue Resource Pool Block (Discrete Event.lix) (pointed at "PoolName") Activity Multiple Block (Discrete Event.lix)

10 10 Progression An item coming in acquires resources if they are available and is queued up otherwise attributes can be automatically set that identify both the pool and the number Once an item has resources, it enters the Activity Multiple block, which simulates a service delay for as many items as specified in the block s dialogue When an item exits through the Release Resource Pool block, its resources are added back to the Resource Pool(s) The number of resources added back is determined from the criteria set up via the Release Resource Pool dialogue When items are allocated varying amounts from a resource pool, or draw resources from more than one pool, it is advisable to maintain this information via the attributes that the Queue Resource Pool block makes provision for the Release Resource Pool is configured via its dialogue to handle a named pool varying resource amounts can be released by using attributes

2008 Winton. Multi Queue Multi Server Model

2008 Winton. Multi Queue Multi Server Model 1 Multi Queue Multi Server Model 2 SQSS to SQMS Model Add servers in the form of Activity Delay blocks (Discrete Event.lix) Or replace the Activity Delay block that models a single server with an Activity,