MES, ERP, APS: who does what in production management?
In short — The ERP decides what to produce and with which resources; the APS decides when and on which machine, based on real capacity; the MES runs execution on the shop floor and reports what actually happened. The three are complementary. Problems almost always arise at the boundaries.
Three systems, three time horizons
| ERP | APS | MES | |
|---|---|---|---|
| Question | What to produce, buy and stock? | When, and on which resource? | How is production running, right now? |
| Horizon | Months and weeks | Weeks, days, hours | Hours, minutes, real time |
| Capacity | Usually infinite | Finite (machines, tooling, staff, materials) | Actual, as observed |
| Typical functions | Orders, purchasing, inventory, costing, material requirements planning (MRP) | Scheduling, scenario simulation, priority management | Work order release, tracking, traceability, quality, OEE |
The ERP is the management backbone: it turns customer orders and forecasts into manufacturing and purchasing requirements. Its requirements calculation usually assumes infinite capacity: it says what should be produced, not whether the shop floor can actually do it.
The APS (Advanced Planning and Scheduling) takes over where the ERP stops: it builds a realistic, finite-capacity schedule that accounts for machines, tooling, skills and material availability. It also lets you simulate: what happens if this urgent order jumps the queue?
The MES (Manufacturing Execution System) runs at the pace of the shop floor: it releases work orders, guides operators, collects quantities, times and stoppages, records lot traceability and calculates performance indicators such as OEE.
How data flows
The reference model, based on the ISA-95 standard, works as follows:
- The ERP sends planned work orders, bills of materials and routings.
- The APS schedules them on resources and returns a detailed schedule.
- The MES executes that schedule and continuously reports progress, consumption, scrap and downtime.
- This feedback updates the ERP (inventory, actual costs) and the APS (rescheduling).
When this loop works, the schedule reflects the real shop floor and inventory reflects real consumption.
The most common pitfalls
- Duplicate functions. Many ERPs have a planning module, and many MES have a scheduling module. Without a clear decision, two schedules coexist and nobody knows which one to trust.
- Poorly shared master data. Items, bills of materials, routings and resources must each have a single master system. A routing changed in the MES but not in the ERP distorts costs.
- Underestimated interfaces. The real-time pace of the MES and the slower rhythm of the ERP do not connect without rules: exchange frequency, error handling, recovery after an outage.
- Starting with the software. Choosing a tool before describing the target processes leads to costly custom development.
Where to start?
- Map current planning and execution processes, and the pain points.
- Decide which system owns what: which system holds bills of materials, routings and the reference schedule.
- Prioritise by expected value: regulatory traceability, on-time delivery, productivity.
- Start with a pilot scope (one line, one workshop) before rolling out.
Our approach
CNEXT supports manufacturers across the whole chain: ERP–APS–MES architecture design, solution selection, integration and change management. Our consultants work on each building block, which avoids blind spots at the boundaries.
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