The Scheduler uses three types of rules to allocate resources for working on an operation:
Sequencing Rule: Sequences the waiting requests in a resource's request queue. For example, "loads for operations with the earliest due dates are listed first." By default, the rule is First In First Out (FIFO). You define this rule for each resource on the Resources form.
Selection Rule: Controls how the resource selects the next waiting request from the queue. For example, "select the load with the least setup time based on the first downstream operation." By default, no selection rule is defined and requests are selected in the sequence they appear in the request queue. You define this rule for each resource on the Resources form.
Resource Group Member Allocation Rule: Controls how the Scheduler selects a resource from a resource group to allocate to a load. For example, "select the resource that has been idle the longest." By default, the resource listed first in the resource group record is selected first. You define this rule for each resource group on the Resource Groups form.
NOTE: When a load arrives at an operation, the Scheduler requests all required resources in the required resource group, forcing each to check its request queue only after all loads scheduled at the same time have arrived. This prevents a lower-priority load from allocating a resource because it arrives when the resource is available, even though a load with higher priority is scheduled to arrive at the same time.
You are not required to use all of these rules. In most cases, the default rules are appropriate and efficient; however, you can define the rules as needed to model your production situations accurately.
If the provided rules do not meet your needs, you can write and custom rules and integrate them into the Scheduler. For each of the rules described above, several rule positions are reserved for your custom rules. See Writing Custom Scheduler Rules for more information.