Elements of the Job Shop Scheduling Problem
a hospital may be organized by Function: the examination rooms are separate from the x-ray room, which is separate from the waiting room. Depending on the needs of the patient, different jobs are performed at different physical locations within the ER, and in some cases. at locations within the hospital other than the ER. A riding academy not only boards and exercises the horses, but also provides lessons at different levels to different groups. A ski resorts similarly provide different levels of instruction for different students. The kitchen of a restaurant is also a job shop-different orders come in at different times and the different meals may be prepared by different people. But all these examples share some common elements:
• The "jobs"-whether they are riding students at an academy or orders for dinner at a restaurant-arrive at the job shop in some pattern. • The ability of the job shop to complete these "jobs" in a given amount of time is dependent upon the capacity or "machinery" in the hope. For example. the number of students who may take riding lessons is limited by the number of horses present at the riding academy; the number of students who enroll in a given may be limited by the number of seat available in the classroom. The ability of the job shop to complete these "job also dependent on the ratio f skilled workers to "machine ." A riding academy may have lots of horses. but the number of riding students is also limited by the availability of skilled instructors. The number of meals that can be prepared in a timely fashion at a restaurant can be limited by the number of chefs working that evening (in addition to the number of ovens, stoves, and other cooking equipment that are available). flow pattern of jobs through the shop varies from job to job. At a restaurant, one order might be for a sandwich and salad while another might be for a full seven-course dinner. Consequently, the number and sequence of steps required to fill these two orders is dramatically different. • Different jobs are often assigned different priorities. Some jobs are marked "rush" or"urgent' ana may be horn a preierred customer. Medical personnel at the ER in the hospital assign these priorities by performing triage so that the most serious patient" are treated first. • The criteria used to evaluate a given schedule differ from Josh shop to re tyrant may try to minimize the wasted food or the idle personnel.
Job Arrival Patterns Jobs often arrive in a pattern that follows a known statistical distribution (for example, the Poisson distribution is relatively common). or they may arrive
in batches (also called "lot" or "bulk" arrivals). or they may arrive such that the time between arrivals is constant. Further. jobs may come with different priorities.