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What is Advanced Planning and Scheduling?

Advanced Planning and Scheduling (APS) refers to a generation of planning and scheduling software beginning in the mid-1990s that simultaneously consider both resource availability and inventory constraints to create achievable schedules and function as a decision support tool.

While advanced planning and scheduling tools have recently appeared that specialize in a variety of applications, the core application of advanced planning and scheduling is the manufacturing industry.

Advanced planning and scheduling evolved out of the older field of "manufacturing scheduling" or "production scheduling", and the distinction between these terms is very much blurred. The fact is that the concept of using software for calculating order and operation start times so as to optimize inventory levels and resource usage while keeping the whole enterprise focused on serving customers in a timely manner is an ancient concept, dating from the early MRP era of the 1960s, and had long been the holy grail of manufacturing IT due to the enormous complexity of the problem.

Early solutions were based on concepts of time buckets and fixed lead times (the idea behind MRP) and ignored even the most basic constraints of resource capacity, leading to unachievable schedules even when the lead times were generously padded to many times their theoretical value and large amounts of inventory were held as buffers. This is still the basis on which the manufacturing modules of ERP systems work today.

The term "production scheduling", however, is most commonly associated with the next generation of software that came to market in the late 1980s and used the technique of "finite capacity scheduling" (FCS) to actually consider the loads on machines or workcenters and output a sequence in which operations could theoretically be performed. Even so, the early finite capacity schedulers depended on MRP being performed externally ahead of time and simply sequenced operations within the bounds of the earliest start and latest end dates output by the MRP system, thus inheriting the fundamental limitations of the older technology.

In the mid-1990s, when the proliferating Windows-based PCs had acquired sufficient processing power to be used for industrial-strength applications, graphical production scheduling systems finally became practicable, and several of the leading production scheduling vendors independently developed capabilities to bypass the inaccurate earliest start and latest end dates calculated by the MRP system by directly considering inventory levels as well as resource loads when scheduling manufacturing orders. Equally important, the use of PCs enabled displaying the schedule graphically in the form of Gantt charts, and the schedule could be modified by the user by dragging and dropping with the mouse. This is when production scheduling stopped being a black box calculating schedules opaquely on questionable assumptions, and started being true decision support tools that empowered humans rather than trying unsuccessfully to replace them. It was around this time that the term "advanced planning and scheduling" was coined to express how much the capabilities of production scheduling software had progressed.

The category remains elusive, however, as advanced planning and scheduling vendors continue to make new breakthroughs in constraint modeling, scheduling logic, and usability that open up new opportunities for profit increase in the user enterprise and make the software applicable to industries and companies for which it had been traditionally considered impracticable.

Currently scores of solutions are marketed under the name "advanced planning and scheduling", but the functional gap between vendors is large and makes the difference between success and failure for many companies. See differentiating capabilities of modern APS software.

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