Manufacturing Execution Systems (MES) deliver the information required for factory personnel to effectively manage the manufacturing process from order launch to the production of finished goods. The MES layer, which is responsible for managing the factory, sits below the ERP, which manages the business.

There are many common information requirements shared by the ERP and MES. An example is raw material inventory data. The ERP needs to know current raw material levels for inventory valuation purposes and for advanced planning. The MES needs to know current raw material inventory levels so that it can dispatch the correct raw materials to the correct work center at the right time. The difference has to do with the granularity of the information that is required. For the ERP, knowing the total on-hand inventory for each raw material is sufficient - it can use this data to calculate the current value of the inventory, and to plan future allocations of material to production. However, for the MES, this degree of detail is insufficient.

In order to optimize inventory usage, the MES needs to know each individual sub-lot of inventory, its quantity, its location, and its current status. 

There are significant business benefits to well-implemented ERP-MES integration: lean business processes that flow seamlessly across the ERP-MES boundary; data synchronization, so that the plant is always making product according to current specifications and the ERP can always plan based on current and accurate information from the shop floor. 



Current product offerings from the major MES and ERP providers support the ERP-MES interfaces defined in the ISA-95 standard and implemented in the B2MML (Business to Manufacturing Markup Language) schemas published by the World Batch Forum. Integration generally focuses on the Production Operations Management aspect of MES, as shown below:

Inside of the MES layer (Level 3 in ISA-95) there are four major areas of functionality:



Determining how to make the product

Determining what the plant is capable of producing with the resources that are available

Determining when and where to make product

Tracking how and where the product was actually made

Each of these areas has an interface to the ERP. Product definitions (BOMs, routes, specifications, etc.) comes from the ERP down to the MES; the MES informs the ERP about the plant's capabilities so that the ERP can plan appropriately; high-level production plans are passed down to the plant layer so that production can be scheduled against specific resources at a specific time; and information on how the product was made is passed back up to the ERP for planning, customer information and accounting purposes.