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268
Resources and Shifts
Resource requirements
Resource requirements
The final step is to create the actual resource requirement – what the Queue requires so that it can let its items leave and continue traveling through the model. Resource requirements are logical expressions consisting of one or more quantity expressions combined using AND/OR operators in conjunction with grouping parentheses.
The Create/modify resource require-
ments frame (Resource Manager’s
Requirements tab) is for specifying
what resources are required for items
to leave the Queue. The result is saved as a resource requirement.
Resource requirement rank
When it is created, each resource requirement gets a resource requirement rank. The resource requirement rank must be  0; the default rank is 1. This ranking is used for sorting items that are waiting for resources, as discussed in “Resource allocation policy” on page 261. It can be overridden for a particular resource, as discussed in “Overriding the resource requirement rank” on page 262.
Creating a resource requirement
On the Requirements tab, enble the Create/modify resource requirements frame. Then either choose an existing resource requirement from the popup menu and modify it or create a new one.
To create a resource requirement, either choose a quantity expression from the popup menu or start with a grouping operator. Use the AND and OR operators between quantity expressions; use the grouping operators to group quantity expressions. The resource requirement rank can be changed from the default of 1.
Example
The tutorial on page 254 showed how to create a resource requirement. To determine if the expression selects the resources that are wanted, use the Test button.
Saving
A new or modified resource requirement won’t be available for use until the Save or Save As button has been clicked. Until the resource requirement is saved, its name will be displayed in red.
☞ Saving the resource requirement saves it to a database. To save the database, save the model.
Default resource requirements
Under certain circumstances the ARM system creates a default resource requirement. In some cases this is done automatically and in other cases it is optional.
The circumstances when a default resource requirement could be created are: • Every time a new pool is created using a Resource Pool block
• Optionally when a new pool is created using a Resource Manager block
• Optionally when a new group is created using a Resource Manager block
• Optionally when a new quantity expression is created using a Resource Manager block
Discrete Event


































































































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