The shortest processing time rule is a prioritization rule that assigns the highest priority to the job that requires the least amount of processing time. This rule minimizes the average flow time of jobs and reduces the number of jobs in queue. The critical ratio rule assigns priority based on the ratio of time remaining until the due date to the remaining processing time. The fewest operations remaining rule assigns priority based on the number of remaining operations for each job. The first come, first served rule assigns priority based on the arrival time of the jobs. References: Managing Supply Chain Operations, Chapter 9: Scheduling and Sequencing, page
237. Manufacturing Planning and Control for Supply Chain Management: The CPIM Reference, Second Edition, Chapter 13: Scheduling and Execution, page 419.