Priority Rules
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Priority Rules

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Priority Rules
    What are Priority Rules         quespin.gif (22297 bytes)
2.    Types of Priority Rules
    Example with Demo Solution1
   Example with Demo Solution2

1.    What are Priority Rules    quespin.gif (22297 bytes)

                Priority rules provide guidelines for the sequence in which jobs should be worked.
        The rules generally involve the assumption that job setup cost and time is independent of
        processing times. In using this rules, job processing times and due dates are important pieces
        of information. Job times usually include setup and processing times. Due dates may be the
        result of delivery times promised to customers, MRP processing, or managerial decisions. The          rules are especially applicable for processs-focussed facilities such as clinics, print shop and
        manufacturing job shops. Priority Rules try to minimise completion time, number of jobs in the
        system, and job lateness, while maximising facility utilisation.

                The following standard measures of schedule performance are used to evaluate
                Priority Rules:

        paw_gr.gif (128 bytes)    Meeting due dates of customers or downstream operations.
        paw_gr.gif (128 bytes)    Minimising the flow time(the time a job spends in the process).
        paw_gr.gif (128 bytes)    Minimising work-in-process inventory.
        paw_gr.gif (128 bytes)    Minimising idle time of machines or workers.

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2.    Types of Priority Rules
      The most popular Priority Rules are:

FCFS (First Come First Serve)
--- The first job to arrive at a work centre is processed first.
EDD (Earliest Due Date)
--- The job with the earliest due date is selected first.
SPT (Shortest Processing Time)
--- The shortest job are handled first and completed.
LPT (Longest Processing Time)
--- The longer, bigger jobs are often very important and are selected first.
CR (Critical Ratio)
--- Critical Ratio is an index number computed by dividing the time remaining until due date
        by the work time remaining.


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