Conventional Priority Rules

 The standard solution for production scheduling (routing and sequencing) difficulties is the utilization of priority rules. A priority rule is an ordering of the queues opposite the machines, as per to similar parameter that is evaluated from the available information about respective job or operations.  Priority rules are simple to know and easy to implement, that illustrates their widespread utilize. A huge number of priority rules have been  proposed  in  the  literature,  but  consequently  far,  no  comprehensive  study  exists  that compares the quality of these rules for a realistic FMS over the complete range of operational situations (time and load pressure levels). Accordingly, contradictory results have been recorded. One of the major results that can be inferred from the literature is which the rules can be categorized into two categories as:

(a) Rules that attain a minute value of the average tardiness but under high pressure produce extremely large delays of a minute fraction of jobs, and

(b) Rules  that  can  ignore  excessive  delays  at  the  cost  of  a  markedly raised average tardiness.

The best identified representative of the initial class is the SPT that is shortest processing time first rule (that we all tend to utilize to ignore the overflow of our desks), but the EDD rule (earliest due date initial) relates to the initial class.