ERP vs POM (MES)

I had long discussion today about when an ERP can used for work order execution and tracking versus and production operations management (POM) systems (as defined by ISA 95 and formerly know as MES). Basically, lets summarize. An ERP is a financial ledger and material and asset planner and manager. An operations management system has to define a product's recipe and/plant routing to a level at which it can be executed. The operation execution requires the ability to validate a bill of materials (BOM), work instruction, QA specification and qualified equipment, material and personnel for each step, cycle or operation of that definition. The hard part is the execution of the business rules around the disposition of work in process material and balance of available resouces downstream. The developing generation of ERP (Gartner calls this ERP2) can do this for a make-to-stock low-to-medium volume noncomplex, low-SKU-count plant environment. Why? This enviroment is predictable and steady-state. When any thing gets unpredictable and has an unsteady state work flow, a real-time transactional database application AT THE PLANT is required. So when a plant makes even as little as 20% of its volume as make-to-order, the line balancing and work flow has to be managed, since the following are subject to constant real-time change: BOM, work instructions, equipment parameter, QA specifications, WIP and resource business rules and scheduling constraints. All of this requires application changement in relatively near real time. So the answer to the ERP vs POM (MES) answer is "It depends."