ISA-95 and the MES-ERP Boundary: What Each System Actually Owns
ISA-95, formally published as International Electrotechnical Commission 62264, defines how enterprise systems integrate with manufacturing systems.
At its core, it answers a practical architectural question:
Where does ERP stop, and where does MES begin?
In the ISA-95 layered model:
- ERP operates at Level 4, responsible for business planning and financial governance.
- MES operates at Level 3, responsible for manufacturing execution, sequencing, and traceability.
When that boundary is clear, execution is disciplined and audits are defensible. When it is blurred, reconciliation work multiplies and evidence weakens.
The Boundary in Plain Language
ERP plans production and accounts for it.
MES executes production and proves it happened correctly.
ERP creates production orders, allocates materials, and manages cost and delivery commitments. MES dispatches work, enforces operational rules, captures time stamped execution data, and maintains genealogy records.
That separation is operational, not theoretical.
How ISA-95 Defines the Relationship
ISA-95 provides standardized models and terminology so business systems and manufacturing systems use consistent definitions.
The model defines:
- Level 4: Business planning and logistics
- Level 3: Manufacturing operations management
ISA-95 does not prescribe specific software. It defines responsibilities and information exchange between layers. That distinction protects system clarity.
ERP Responsibilities at Level 4
ERP governs planning and financial accountability.
In practice, ERP owns:
- Production order creation and release
- Bill of materials governance
- Inventory allocation and accounting
- Cost tracking and margin reporting
- Delivery commitments and forecasting
ERP answers the question:
What should be built, when, and at what cost?
MES Responsibilities at Level 3
MES governs real time execution and operational traceability.
In practice, MES owns:
- Dispatching work to equipment and operators
- Enforcing operation sequence
- Real time consumption tracking
- Capturing execution events with timestamps
- Recording genealogy and quality evidence
MES answers the question:
What actually happened on the floor, and can we prove it?
Why This Separation Matters
When ERP attempts to manage execution state directly, or MES starts embedding business logic that belongs in ERP, predictable problems appear:
- Conflicting order status between systems
- Manual reconciliation processes
- Duplicate data ownership
- Retroactive corrections instead of governed execution
- Weak audit evidence
In regulated environments, execution state must reflect real time control, not after the fact adjustment.
ISA-95 reduces these risks by clarifying:
- Which system owns which data
- When transactions occur
- How structured objects cross the boundary
The Role of Standardized Transactions
ISA-95 defines object models and business to manufacturing transactions.
Many integrations implement these models using B2MML, which provides schemas aligned to ISA-95 definitions.
Using standardized object models:
- Prevents custom undocumented interfaces
- Reduces ambiguity during audits
- Improves long term maintainability
- Ensures both systems interpret data consistently
Structured transactions create governance at the integration layer.
Common Architectural Failure
A common failure mode is shifting logic across the boundary for convenience.
Examples include:
- Allowing ERP to update execution state without MES validation
- Embedding costing logic inside MES
- Maintaining duplicate master data ownership
- Correcting production history retroactively
These shortcuts accumulate technical debt and compliance risk.
Good architecture enforces:
- ERP as the authority for planning and master data
- MES as the authority for execution control
- Clearly defined transaction contracts between them
Concrete Regulated Example
In an aerospace production environment:
- ERP releases a production order with BOM and schedule.
- MES receives the order and dispatches operations.
- Operators execute tasks under controlled sequencing rules.
- Time stamped execution data and genealogy are recorded in MES.
- Structured completion transactions are sent back to ERP.
ERP reflects production status based on governed execution events, not manual updates.
This alignment supports traceability from financial planning through physical production.
Key Takeaways
- ISA-95, also known as IEC 62264, defines the integration boundary between ERP and MES.
- ERP governs planning, master data, and financial accountability at Level 4.
- MES governs real time execution, sequencing, and traceability at Level 3.
- Blurring system responsibilities creates reconciliation work and audit risk.
- Standards such as B2MML implement ISA-95 object models for structured integration.
Technical Next Steps
Architects implementing MES-ERP integration should:
- Explicitly document system ownership of master data
- Map ISA-95 object models to integration contracts
- Prevent retroactive execution updates from bypassing MES governance
- Define transaction timing across the Level 3 to Level 4 boundary
Clear boundaries are not bureaucratic overhead. They are operational control.