MES versus ERP integration: a practical ownership checklist

MES and ERP integration becomes difficult when both systems claim to own the same fact. “The order status,” “the material quantity,” and “the production count” sound singular until the teams compare definitions, timestamps, corrections, and responsibility. A useful interface begins with ownership, not with a list of endpoints.

Give every fact a home

ERP usually owns business orders, financial inventory, procurement, and enterprise master data. MES owns the executable production order, dispatch, work instructions, genealogy, quality checks, and the production result at the plant. Control systems own live states and measurements. The historian keeps time-series evidence. These boundaries are not universal, but each site should write its own version and make exceptions explicit.

Use the ISA-95 vocabulary to name the objects crossing the boundary: personnel, equipment, material, process segments, schedules, and performance. The ISA-95 levels guide is a useful starting point, but a standard model still needs plant-specific identifiers and units.

Design events and corrections

Prefer business events with clear ids and timestamps over a shared table that every system edits. An ERP release can create or update a production order; MES can acknowledge it, dispatch operations, and report actual quantities; ERP can post the business result. Define whether messages are at-most-once or replayable, how duplicates are recognized, and who can correct a late result.

Separate event time from processing time. A gateway or MES may be offline while production continues, so the time a result happened is not the time the ERP received it. Carry source system, version, unit, reason code, and correlation id through the interface.

Test the uncomfortable cases

• An order is changed after the first operation has started.
• A material lot is substituted and later recalled.
• A machine reports a count after the MES connection was down.
• Quality rejects part of a lot and reworks the rest.
• The same message is delivered twice or arrives out of order.
• A shift ends across midnight and both systems disagree about the date.

Put reconciliation on an operations dashboard. “Interface healthy” should mean business facts agree, not merely that an HTTP request returned 200. When production data needs more context, SCADA, MES, and historian: where each one ends shows the boundaries in plain language.

For a wider systems map, Understanding the Shop Floor is a practical companion ebook.