MES Requirements: Definition, Structure, and Typical Content

MES requirements describe the functional, technical, and organizational criteria a Manufacturing Execution System must fulfill to fit a company's processes, IT landscape, and strategy. The term appears most commonly in three contexts: MES selection (RFI/RFP), creating a requirements specification, and defining a rollout blueprint for multiple plants.

Functional Requirements

Functional requirements define what the MES must do. Typical topics include production data collection (quantities, times, machine states, OEE), order management (ERP download, sequencing, feedback), traceability and genealogy (batch, lot, or serial number tracking), quality management (inspection plans, in-process checks), operator guidance (digital work instructions, variant-specific steps), and resource and equipment management.

Not every plant needs every function. The key is to prioritize the most important use cases – such as OEE and downtime monitoring, traceability, or digital shopfloor – and focus requirements accordingly.

Technical and Integration Requirements

Technical requirements determine whether an MES fits the existing IT landscape:

Architecture: On-premises or cloud/SaaS MES, multi-tenancy, multi-site scalability.

Interfaces: ERP (SAP, MS Dynamics) for orders and master data, machine connectivity via OPC UA or MQTT, integration with CAQ, WMS, PLM, and BI platforms.

Data model: Consistent IDs for orders, machines, materials, batches, and serial numbers as the foundation for cross-plant analytics.

Security and compliance: Audit trail, role management, OT security, network segmentation – plus any requirements from NIS2 or ISO 27001.

Structure of an MES Requirements Specification

A solid specification doesn't contain 300 bullet points where 80% go unused. It contains a prioritized, business-relevant requirements list:

1. Current situation and objectives – today's problems and a concrete target picture
2. Scope – plants, lines, timeline
3. Functional requirements – by topic, each rated as Must / Should / Nice-to-have
4. Technical and integration requirements – target architecture, interfaces, IT security
5. Non-functional requirements – availability, response times, usability
6. Project and support requirements – implementation model, SLA, release cycle

Common Mistakes

Too vague: "The system must be user-friendly" tells no one anything. Concrete means: touch operation on the shop floor, maximum booking time of X seconds, mobile access for maintenance teams.

No prioritization: When everything is equally important, no vendor can deliver a meaningful fit/gap assessment.

IT-only or operations-only: MES sits between OT, IT, and operations – both perspectives must be represented.

Forgetting data and reporting: Functions described, but no requirements defined for KPIs, data history, or data access.

FAQ

How detailed should MES requirements be? Detailed enough to clarify use cases, KPIs, and integration needs – but not so detailed that the vendor's solution design is predetermined. What and why belong to the customer; how is the vendor's job.

What matters more: functions or integration? In practice, interfaces, data model, and rollout capability are often more critical than individual features. Without clean ERP and machine integration, even strong MES functionality delivers little value.

Does each plant need its own requirements? No. A central core template extended by a few local specifics is the right approach – it keeps the system manageable both technically and organizationally.