MES is a loaded term. Ask two people in manufacturing to define it and you’ll likely get two different answers. The definition will depend on their vertical, current vendor, and which type of manufacturing operations they run.

This is because the acronym, which stands for Manufacturing Execution System, was coined after the underlying technology emerged and it quickly became a buzzword. As vendors jumped on the bandwagon, calling their disparate solutions ‘MES’, the term became diluted.

In this post, we’ll delve deep into the attempts from organizations such as the Manufacturing Enterprise Solution Association (MESA) and the International Society of Automation (ISA) at standardizing the definition to make it less trivial.  

Understanding these models and standards can help you better understand manufacturing execution systems and evaluate their modern alternatives.

The MESA Model – defining MES by function

The most widespread definition of MES is perhaps the MESA model, which defines MES by function areas.

MESA, was created in the 1990s to advise on the execution of MES systems and address their growing complexity.


In 1997, MESA formally defined the scope of MES through 11 core functions, called the MESA-11 model. These functions stem from the view of a plant and include:

  1. Operations/Detailed Sequencing
  2. Dispatching production units
  3. Product tracking and genealogy
  4. Labour Management
  5. Quality Management
  6. Maintenance Management
  7. Resource allocation and status
  8. Document control
  9. Performance Analysis
  10. Process Management
  11. Data Collection and Acquisition

In 2004, the model’s focus increased to include business operations. In addition to core operations, the model included focuses like supply chain optimization and asset optimization. This an update is the Collaborative MES, or C-MES.


According to MESA, this model focused on how core operations activities interact with business operations. The model takes into account increased competition, outsourcing, supply chain optimization, and asset optimization.

The C-MES interfaces with other business operation areas around the edges. These include supply focused systems (Procurement SCP); customer-focused systems such as CRM and service management; financial and performance focused systems such as ERP and Business Intelligence BI software; product-focused systems such as CAD/CAM and PLM; logistics systems such as TMS and WMS; controls (PLC, DCS); and compliance systems (DOO management, ISO, EH&S).

Mesa Model

Finally, in 2008, the model was expanded to its current version, which spans from production, to plant operations, to business operations, and even to strategic initiatives such as lean manufacturing, quality and regulatory compliance, product lifecycle management, real-time enterprise, asset performance management, and others.

At its core, MESA’s definition of an MES is a functional definition based on the different functions an MES should serve. In order for a system to be an MES, it must have all the functional groups or a reasonable combination of them. But the definition has evolved over time. With C-MES, the MES served as an intermediary between automation and corporate management, and also as a data and information hub. It is not only a collection of functions but an integration hub for information throughout the company.

ISA-95 defining MES by information architecture

ISA-95 was jointly developed by the International Society of Automation (ISA), formerly known as the Instrumentation, Systems, and Automation Society, and the American National Standards Institute (ANSI). The development of the ISA-95 standard began in 1995 when computers began to penetrate manufacturing’s information and control systems.


ISA-95 Model

Unlike the MESA model, which focused on business process, the ISA-95 model focuses on information architecture. The ISA-95 model divides production systems into 5 levels, based on the Purdue Enterprise Reference Architecture (PERA) model.

In this way, the ISA-95 standard helps define boundaries between systems. Intelligent devices, such as sensors, belong to Level 1. Control systems such as PLCs , DCS, OCS, belong to Level 2. MES, belong to Level 3. ERP to level 4.

By situating MES on Level 3, ISA-95 implies that MES connect production with enterprise systems, manage workflows to produce end products, maintain records of production, and optimize the production process.

The goal was to develop a standard that would enable efficient interfacing and integration between an ERP system and an MES. This would facilitate effective communication between stakeholders, lowering the total cost of ownership and enabling error-free integration.

Namur – Defining MES by vertical

As we’ve seen, MESA defines MES by function, and ISA-95 defines it by information architecture. However, since every industry and type of manufacturing operation has different requirements in their manufacturing, quality, business processes, and regulatory environment, MES vary by industry and type of manufacturing operations.

There have been industry-specific attempts at standardizing MES definitions. NAMUR, for example, is a group of end users particularly involved in the process industry (chemical and pharma for the most part). Their recommendations are based on ISA-95, but the group makes more concrete definitions for their industry’s needs.

On a broader level, we can distinguish between Process and Discrete industry verticals. Naturally, each type of operation has a different set of requirements, so an MES serving each one will differ in important ways.

Process verticals thus view MES as the machine and plant control systems. While discrete industries view the MES as more of an online information system, a feedback and control system for production.

Other attempts to define MES

In addition to the standards we’ve covered so far, there are other standards such as the VDI standard. The VDI standard was developed by the Verein Deutsche Ingenieure in 2004 on the basis of the standards we covered above. As with all standards, the goal of VDI was to give MES a fixed meaning that would prevent vendors from trivializing the term for marketing purposes.

Changing Definitions with IIoT

Recently, analysts have observed that MES are moving toward an applications and micro-services model. As a result, MES vendors are starting to move away from a position as all-encompassing solutions. Instead, they’re experimenting with selling modularized functionality. With the emergence of IIoT, many have even begun to question whether MES are still relevant in the digital era. Right now, the market is still evolving. But it will be interesting to watch which direction it moves in the next five years. IIoT applications? Traditonal MES? Or both?

Beyond standards and models

As you can see, there have been multiple attempts to standardize the MES definition. For the subject matter expert, these standards and models might be useful. However, for the regular end user of MES, they can be more confusing than illuminating. Perhaps a better way to define manufacturing execution systems is by the common features they tend to have, usually around 5 main areas: production functions, quality, human resources, data collection, and systems integration.

Manufacturing Execution Systems are complicated pieces of software. If you’d like to understand all about them, we’ve prepared the ultimate guide. You can download it for free by clicking the image below.