Rockwell Automation FactoryTalk Scheduler Users Guide - Manual (Page 56)

F ACTORY T ALK S CHEDULER U SER ’ S G UIDE
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Tardiness, Minimum Job Flow Times, and Maximum Facility Capacity. We will
discuss each of these core objectives and the corresponding FactoryTalk Scheduler
operation and resource selection rules that support these objectives.
This categorization of the rules should help you narrow your choices based on your core-
scheduling objective. The selection of a specific rule within a category is based on the
specific nature of the scheduling problem, the importance of a “good” schedule, and the
time available for generating schedules. Each category of rules will contain some mixture
of static and dynamic rules.
Predefined Job Preference
The Predefined Job Preference category of rules is focused on selecting the next operation
based on the predefined job priority or a user-specified property field (e.g., cost). In
general, each of these rules can be invoked by selecting the operation with the highest or
lowest value of this characteristic. This category includes Highest Priority First, Lowest
Priority First, Highest Order Property Field, Lowest Order Property Field, Dynamic
Highest Order Property Field, Dynamic Lowest Order Property Field, Schedule File
Order, Longest Waiting Time, Shortest Waiting Time, and Largest Processing Time.
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The Highest Priority First and Lowest Priority First are static rules that select the
operation with the highest or lowest Priority value, respectively.
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The Highest Order Property Field and Lowest Order Property Field are static
rules that operate similarly to the Priority rules, except that the selection is based on
any user-specified property. The rule selects the job with the highest or lowest value of
this property. For example, the Highest Order Property Field rule using a property
field defined as Cost selects the job with the highest value of Cost. Since this is a static
rule, it is assumed that the value of Cost does not change while the job is waiting to be
processed for any jobstep.
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The Dynamic Highest and Lowest Order Property Field rules are dynamic versions
of the Highest and Lowest Order Property Field rules. Although these rules execute
more slowly, they accommodate situations where the value of the property field may
change while the job is waiting.
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The Schedule File Order rule is a static rule that selects the operation based on the
order that it was entered into the database. This rule is similar to a first come, first
served rule.
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The Longest and Shortest Waiting Time rules are dynamic rules that select the
operation based on the amount of time that the job has been waiting to be scheduled.
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The Largest Processing Time rule selects that operation with the largest processing
time.