Manufacturing Execution System (MES) serves as the link for enterprise CIMS information integration and is a fundamental technical means to implement agile manufacturing strategies and achieve agile shop floor production. This article introduces the concept and functional model of MES, as well as the relationship between MES and ERP and shop floor automation systems, and describes the typical structure of an MES system. 1. Overview Manufacturing is a crucial pillar industry of China's national economy, occupying a central position in the secondary sector. With China's accession to the WTO and economic globalization, China is becoming the center of global manufacturing. Chinese manufacturing enterprises face increasingly fierce domestic and international competition. A key aspect of rapidly improving their core competitiveness is to drive industrialization through informatization, accelerate the informatization process, follow a new path of industrialization, and achieve leapfrog development of overall social productivity. Looking at the current application status of information systems in China's manufacturing industry, the focus is generally on ERP management systems and Shop Floor Control Systems (SFC). However, due to the rapid evolution of product marketing from production-oriented to market-oriented and competition-oriented in the past one or two decades, challenges have been posed to the management and organization of manufacturing enterprises' production sites. Relying solely on ERP and shop floor automation systems is often insufficient to cope with this new situation. Manufacturing Execution System (MES) perfectly fills this gap. MES is a production management technology and real-time information system that has rapidly developed internationally over the past decade, targeting the shop floor level. MES provides users with a fast-responding, flexible, and sophisticated manufacturing environment, helping companies reduce costs, deliver on time, improve product quality, and enhance service quality. It is applicable to various industries (home appliances, automotive, semiconductors, communications, IT, pharmaceuticals) and can provide excellent enterprise information management for both single-product high-volume production and hybrid manufacturing enterprises that combine multi-variety, low-volume production with high-volume production. Currently, the application of MES systems by well-known international companies is widespread, and many domestic enterprises are also gradually adopting this technology to enhance their core competitiveness. 2. The Information "Gap" Between the Enterprise Planning Layer and the Process Control Layer The traditional production process used in China's manufacturing industry for many years is characterized by "top-down" planned production. Simply put, from the planning layer to the production control layer: the enterprise formulates a production plan based on orders or market conditions—the production plan arrives at the production site—production is organized—products are delivered. The focus of enterprise management informatization construction is mostly placed on the planning level for production planning management and general administrative processing. For example, ERP sits at the upper planning level, used to integrate existing production resources and create production plans. At the lower production control level, enterprises mainly use automated production equipment, automated testing instruments, and automated logistics handling and storage equipment to solve specific production (process) bottlenecks and achieve automated control of the production site. Due to changes in the market environment and the continuous updating of modern production management concepts, the key to the healthy operation of a manufacturing enterprise is to ensure close coordination between "planning" and "production," enabling enterprise and workshop managers to grasp changes in the production site in the shortest possible time, make accurate judgments and take rapid countermeasures, and ensure that production plans are reasonably and quickly revised. Although ERP and field automation systems have reached a very mature level, because ERP systems serve the upper management level of the enterprise, they generally do not provide direct and detailed support for workshop-level management processes. The function of field automation systems is mainly to monitor field equipment and process parameters; they can provide managers with field detection and statistical data, but they are not true management systems in the strictest sense. Therefore, a "gap" in management information has emerged between ERP systems and on-site automation systems. These systems often prove inadequate or functionally weak in addressing the scheduling and management requirements at the user's workshop level. For example, they struggle to provide comprehensive solutions to the following typical workshop management problems: • When a user complains about a product, can all production process information for that batch of products be traced based on the product number? Can its: raw material supplier, operating machine, operator, processes performed, production date and time, and key process parameters be immediately identified? • When multiple product models need to be mixed and assembled on the same production line, can automatic verification and operation prompts prevent worker errors in component assembly, product production process errors, product mixing, and incorrect handover of goods? • What are the five most frequent product defects on the production line in the past 12 hours? What is the quantity of each defective product? • What is the current quantity of each product in the warehouse and on the upstream, midstream, and downstream production lines? Which suppliers are they to be supplied to? When can they be delivered on time? • How much time are the production lines and processing equipment in operation, and how much time are they idle or running? What are the main reasons affecting the equipment's production potential: equipment failure? Scheduling errors? Untimely material supply? Is worker training insufficient? Or are process indicators unreasonable? • Can product quality inspection data be automatically statistically analyzed to accurately distinguish between random and abnormal fluctuations in product quality, eliminating potential quality problems at the outset? • Can manual reports be eliminated, and production quantity, pass rate, and defect codes for each process be automatically calculated? The MES (Manufacturing Execution System) is positioned as the execution layer between the planning layer and the field automation system, primarily responsible for workshop production management and scheduling. A well-designed MES system can integrate management functions such as production scheduling, product tracking, quality control, equipment failure analysis, and network reporting on a unified platform. Using a unified database and network connectivity, it can simultaneously provide workshop management information services to production, quality inspection, process, and logistics departments. The system helps enterprises implement complete closed-loop production by emphasizing the overall optimization of the manufacturing process, assisting enterprises in establishing an integrated and real-time ERP/MES/SFC information system. 3. Manufacturing Execution System (MES) and its Functions 3.1 Definition of MES MES is a new concept proposed by the American management community in the 1990s. The Advanced Manufacturing Research (AMR) organization in the United States, through a survey of numerous enterprises, found that existing enterprise production management systems generally consist of enterprise management software represented by ERP/MRPII, production process monitoring software represented by SCADA and HMI (Human Machine Interface), and a suite of MES software to automate operations and support comprehensive enterprise integration. Based on the survey results, AMR proposed a three-tiered enterprise integration model in 1992 (as shown in Figure 1). MESA International (MES International Federation) is a trade federation dedicated to promoting MES concepts and products. It has developed a series of research, analysis, and development plans to help its member organizations promote MES in the business world. The MESA White Paper No. 6 (1997) defines an MES system as follows: • An MES system acts as an information transmitter for optimizing production activities throughout the process from work order issuance to finished product output. • When events change, MES enables rapid responses by leveraging real-time, accurate information, MES specifications, original work status, data feedback, and other data to reduce non-value-added production activities and improve the efficiency of factory production processes. • MES improves production conditions, on-time delivery, inventory turnover, production profit, and cash flow efficiency. MES also provides a two-way flow of production information between the enterprise and the supply chain. The MESA White Paper No. 3 (1997) describes the operational interaction and information flow patterns between Enterprise Resource Planning (ERP), MES, and control systems, as shown in Figure 2. On the left side of the figure, ERP and other systems need to constantly monitor product inventory levels, customer order status, and material requirements, then transmit this information to MES, which executes production or arranges inventory to meet customer order demands. For MES, this layer is the production planning layer. The middle part is the MES system, responsible for completing product manufacturing. Product specifications, models, parameters, and other relevant data are stored in this system. MES transforms this product-related data into operating procedures for use by operators or machinery in the control system. The right side represents the control system. Once the work procedures, related processes, documents, and other relevant production requirements are ready, the control system utilizes all relevant resources within the factory (software, hardware, and personnel) to complete the manufacturing process and achieve the product production goals. 3.2 MES Functions As can be seen from the definition of MES, it is a series of management functions, not a single software system. It can be a collection of various production management functional software. MESA, through the practices of its members, has summarized eleven main MES functional modules, including: detailed process scheduling, resource allocation and status management, production unit allocation, process management, human resource management, maintenance management, quality management, document control, product tracking and product list management, performance analysis, and data acquisition. The relationship between the various functional models of MES and other enterprise information systems is shown in Figure 3. Actual MES products may simultaneously include one or more of these functional modules. 4. Typical Structure of MES Since MES plays the role of "information transmitter" for optimizing production activities throughout the entire process from work order issuance to finished product output, it must possess multiple functions and simultaneously serve multiple departments such as production, quality inspection, process, and logistics. This dictates that the structural design of MES must meet the following principles: • MES should be a distributed computer system. • The MES system can connect with other manufacturing information systems within the enterprise, thereby providing efficient enterprise management functions. • "It takes production behavior information as its core and provides direct support for the enterprise decision-making system" (MESA 1997). Because factories may purchase suitable MES modules from different software vendors or integrate various existing management systems in the workshop into the MES functionality, many factories' MES systems are essentially a hodgepodge. Each system has its own processing logic, database, data model, and communication mechanism. Furthermore, because MES applications are often task-critical systems, such systems are difficult to upgrade with technological updates. A MES system based on a unified hardware and software platform typically uses industrial PCs/PLCs/HMIs as the main components of functional stations in each production unit (production area) within the workshop. Through data collection and feedback from each production unit, it forms an open Ethernet network covering the entire factory or production line, meeting the needs of closed-loop production management. An MES database server is used as the system core for real-time data storage and comparison, enabling monitoring, control, and management of production information and processes. The system is designed based on large-scale relational database technology, facilitating the storage, comparison, and processing of large amounts of real-time data, generating various statistical analysis reports, and providing standard internet browsing, querying, and remote data retrieval based on stable web applications. A typical current MES architecture model is shown in Figure 4. Within the enterprise, each functional station interacts with the MES server via a local area network (LAN), while other query terminals also query the data, reports, and graphs provided by the MES after processing via the LAN. Externally, the MES can be connected via the Internet, allowing users to publish or read information within designated permissions. The company's internal management, external agencies, and other related business units are connected through MES to form a close-knit whole, achieving real-time information sharing and making business processes orderly and efficient. 5. MES and ERP: Although ERP and MES are highly complementary in function, they do not necessarily need to depend on each other during enterprise informatization. In areas such as production planning management, quality management, and logistics management, the functions of MES and ERP systems can be extended and integrated to jointly build a more complete modern enterprise information management system. When an enterprise already has an ERP system, MES can be integrated with the ERP system to optimize the company's information management and more effectively ensure the achievement of business goals. The advantages of integrating MES and ERP systems are: • Further improving existing operating processes, achieving unified standardized operation between enterprise management and workshop management, thereby more effectively shortening product cycles and improving labor productivity. • Further upgrading information technology infrastructure, achieving centralized management of internal information and data, fundamentally reducing the time for internal information and data circulation. • Cooperating with supply chain management (SCM) systems to reduce supply chain costs, enhance rapid response to customer needs, optimize customer service, and improve the company's overall work efficiency. • Enhance the functionality of daily data updates and real-time statistical analysis of management reports in the financial system to achieve the goal of daily closing. • Real-time data-based planning more accurately and timely reflects the overall production situation. 6. The Future of MES MES is a production management technology and real-time information system oriented towards the shop floor level. It is a fundamental technical means to implement an enterprise's agile manufacturing strategy and achieve agile shop floor production. Because MES emphasizes control and coordination, modern manufacturing information systems not only have excellent planning systems but also effective execution systems that ensure plans are implemented. Therefore, in just a few years, MES has been rapidly adopted by foreign companies, bringing significant economic benefits. Chinese enterprises have been implementing enterprise management software, primarily MRPII/ERP, for nearly 20 years. While there are a large number of ERP vendors and development teams in the industry, only a small portion of these vendors are moving towards MES. This is because MES is closely integrated with industrial control, and its research and implementation require a strong foundation in industrial automation and industrial field engineering experience. This presents a high technical barrier, excluding many ERP-type IT vendors. However, we also believe that with the development of the industry and the economy, a considerable number of IT vendors will merge or cooperate closely with automation vendors and manufacturing companies. In 2-3 years, MES vendors may spring up like mushrooms after rain, and their technologies and implementation methods will inevitably become more and more mature.