In shortMES (Manufacturing Execution System) manages and records how production orders are executed on the plant floor and keeps material, equipment, quality and traceability information.
MES manages how the production planned in ERP actually happens on the floor: which order ran on which line with which materials, in what time, and what the quality result was. In the ISA-95 model it corresponds to the operations management layer (level 3).
MES data is usually fed from PLC/SCADA data and returns to ERP as confirmations. In this two-way flow timestamps, units and duplicate checks become critical.
In OPC Router projects
OPC Router can configure shop-floor data flows into MES and between MES and ERP; the scope of MES business logic is defined separately.