Scheduling problems appear in several industries. A manufacturing company must decide the sequence and machines used in the production process of each product; a delivery company must decide on the sequence of customers to visit; a transportation company must determine which of its vehicles to use in the trips.
Take an airline company for instance. How many flights are delayed for uncontrollable issues such as bad weather? Once a disruption occurs, many costs arise: lost revenue, overtime for employees, food and lodging vouchers… and once the bad weather is gone, how to quickly recover back to a normal schedule?
Examples of scheduling problems
The goal of a scheduling problem is to allocate and prioritize demand to available facilities. Demand can either be customer orders, waiting to be fulfilled, or forecasts on the expected future demand. The concept of demand (or tasks to be accomplished) and facilities (or resources to be used) are very broad:
– in computer systems, programs compete for processors and memory
– in construction jobs, the phases of a project compete to be assigned to work teams
– aviation, take-offs and landings compete for runways
– in logistics and factories systems, production operations compete for machines!
In logistics and production systems, the role of scheduling is to decide the sequence, when and on which machines the orders will be processed. How this will be done changes depending on the goal.
– minimize flow times: measured by the time it takes to complete an order
– minimize the makespan: measured by the time it takes to complete a group of orders
– minimize inventory costs: how to schedule orders to have the smallest inventory
– minimize tardiness: measured by the difference between the order’s due date and its real completion time
– maximize the use of resources: keep machines busy at all times!
Now that you know what scheduling is, all you need to do is learn how to sequence activities and how to measure the quality of a scheduling plan. Read our post on sequencing rules and performance indicators for scheduling problems.