5. Rationalising External Systems in S/4HANA Transformations — Why Integration Simplicity is a Strategic Advantage
- David Murphy
- 2 days ago
- 6 min read
Introduction
Integration is often treated as a technical activity. In reality, it’s a design decision that shapes complexity, cost, and delivery outcomes.
This article explores how to approach rationalisation, and the role of MES sequencing in simplifying integration by design.
S/4HANA Transformations Create an Opportunity to Simplify — Not Carry Complexity Forward
Most SAP S/4HANA programmes don't remove complexity — they just relocate it.
S/4HANA transformations rarely exist in isolation. Around the core ERP sits a landscape of external systems — from Manufacturing Execution Systems (MES) to Laboratory Information Management Systems (LIMS), planning tools, and industry-specific platforms.
Too often, these systems are treated as fixed constraints.
Leading organisations take a different view: they use the transformation as an opportunity to simplify the landscape — not carry complexity forward.
The Reality: Complex, Fragmented Landscapes
Most organisations operate with:
Multiple MES platforms across sites or regions
Different LIMS solutions acquired over time
Custom-built integrations between legacy systems
Inconsistent data flows and interfaces
This creates a landscape that is:
Expensive to maintain
Difficult to test end-to-end
Prone to failure at integration points
Slow to adapt to change
When S/4HANA is introduced without addressing this, complexity is not removed — it is carried forward, or amplified.
The Hard Truth: Integration is a Design Decision
Integration is often treated as a technical activity — something to be solved during build.
In reality, it is an architectural decision that should be made early.
By the time integration design begins, many of the decisions that drive complexity have already been locked in:
Multiple systems retained without challenge
Local process variations accepted
No clear target architecture defined
At that point, integration teams are not simplifying — they are connecting complexity.
Why Rationalisation Matters
Integration is one of the biggest hidden costs in any programme.
Every additional system means:
More interfaces to design and build
More scenarios to test
More dependencies during deployment
More points of failure post go-live
Simplifying the landscape reduces:
Development effort
Testing cycles
Operational risk
And critically — it improves speed of delivery.
Think in Layers: Designing the Landscape
A practical way to approach this is to think in three layers:
Core — S/4HANA (finance, planning, core supply chain)
Execution — MES, LIMS, operational systems
Edge — shop floor systems, equipment, IoT
Complexity often sits in the execution layer, but impacts everything above and below it.
Without a clear strategy across these layers, integration becomes fragmented and difficult to scale.
The MES Example: The Power of Standardisation
Manufacturing environments often highlight this challenge clearly.
Where multiple MES platforms exist:
Each requires separate integration design
Interfaces behave differently across plants
Testing must be repeated for each variation
Where a single MES platform is adopted:
Integration can be standardised
Development is reused across sites
Testing is significantly reduced
Support becomes simpler and more scalable
In reality, achieving a single MES is not always immediately possible.
But having a clear strategy and roadmap toward that target state is where value is created.
Without that, integration becomes a series of local solutions rather than a coherent design.
MES and S/4HANA — Getting the Sequencing Right
One of the most critical — and often underestimated — decisions in a transformation is the sequencing of MES relative to S/4HANA.
There is no single answer. The right approach depends on business context, risk appetite, and the current system landscape.
However, three clear patterns emerge:
Option 1. MES Before S/4HANA — Standardise First
This approach focuses on simplifying the manufacturing layer before introducing S/4HANA.
Best suited when:
Multiple MES platforms exist across sites
MES processes are highly inconsistent
Shop floor execution is a major source of complexity
Advantages:
Reduces integration variants before S/4 arrives
Enables standard interfaces into S/4
Simplifies testing and deployment
Risks:
Extends overall programme timeline
Requires strong business alignment early
👉 This is often the best option where manufacturing complexity is the primary constraint
Option 2. MES After S/4HANA — Stabilise Core First
Here, S/4HANA is implemented first, with MES rationalisation following as a second phase.
Best suited when:
ERP is the burning platform (e.g. ECC end-of-life)
MES landscape is relatively stable
Business priority is finance, reporting, or supply chain visibility
Advantages:
Faster path to S/4 go-live
Lower immediate disruption to manufacturing
Risks:
Legacy MES complexity is carried forward
Integration may need to be redesigned later
Potential duplication of effort
👉 This is common — but often leads to missed simplification opportunities
Option 3. MES and S/4HANA in Parallel — Coordinated Transformation
Both MES and S/4HANA are transformed together, aligned to a common target architecture.
Best suited when:
There is strong programme governance
The organisation can handle change at scale
A clear end-state architecture is defined upfront
Advantages:
Integration designed once, not reworked
Maximum alignment to target state
Avoids reimplementation later
Risks:
High complexity in delivery
Requires experienced programme leadership
Increased dependency management
👉 This delivers the best long-term outcome, but only if execution capability is high
How to Decide the Right Approach
The decision should not be driven by technology — but by where complexity sits today.
Ask three key questions:
Q1. Where is the biggest source of variation?
If it’s shop floor execution → prioritise MES
If it’s planning/finance → prioritise S/4HANA
Q2. How standardised are processes across sites?
Low standardisation → MES first or parallel
High standardisation → S/4HANA first is viable
Q3. Can the organisation absorb change at scale?
Limited capacity → sequence (not parallel)
Strong governance → consider parallel
A Practical Principle : If you integrate S/4HANA into a fragmented MES landscape, you are designing complexity into your future state.
Define the Target State — Even If It’s Not Immediate
One of the biggest missed opportunities in S/4 programmes is failing to define a clear end-state architecture.
Instead, decisions are made locally or tactically:
“We’ll integrate what we have today”
“We’ll deal with rationalisation later”
The result is a new core system surrounded by old complexity.
A better approach is to:
Define a target application landscape
Identify which systems should be retained, replaced, or consolidated
Establish clear architectural principles (e.g. standard platforms, minimal variants)
Put governance in place to enforce those decisions
Create a phased roadmap to get there
Even if rationalisation cannot be delivered in the first release, it should still guide design decisions from day one.
Simplifying Integration by Design
With a clear target state, integration can be approached more strategically:
Standardise interfaces wherever possible
Reduce point-to-point integrations in favour of scalable patterns
Align data structures across systems
Avoid customisation that locks in complexity
This ensures that integration is not just built — but designed for simplification over time.
The Trade-Off: Short-Term Effort vs Long-Term Gain
Rationalisation is not always easy.
It often requires:
Challenging local preferences
Aligning across business units
Making investment decisions beyond the core ERP
But the alternative is accepting:
Ongoing complexity
Higher costs
Slower future change
The question is not whether rationalisation is difficult — it’s whether avoiding it is sustainable.
Testing and Deployment: Where Complexity Shows Up
One of the clearest impacts of a fragmented landscape is during testing:
Multiple integration variants increase test scenarios
End-to-end testing becomes harder to coordinate
Defects are more difficult to isolate
Simplified landscapes:
Reduce test cycles
Improve reliability
Accelerate deployment timelines
What looks like an architecture decision early on becomes a delivery advantage later.
Final Thought
S/4HANA programmes are not just about implementing a new ERP — they are about reshaping the technology landscape around it.
External systems like MES, APS, WMS or LIMS are part of that story.
You may not be able to rationalise everything immediately.
But without a clear strategy and roadmap, complexity will persist — and value will be limited.
Sequencing decisions, integration design, and system rationalisation are all connected.
Simplify where you can. Standardise where it matters.
Design today with your future landscape in mind — not your current constraints.
S/4HANA Transformation Series
When “Agile” S/4HANA Programmes Quietly Revert to Waterfall — and Why It Matters
Fit-to-Standard — But Which Standard Are You Actually Choosing?
Why Data Will Make or Break Your S/4HANA Programme — Long Before Go-Live
Right-Sizing Change Management in S/4HANA — Why Timing Matters More Than Headcount
Rationalising External Systems in S/4HANA — Why Integration Simplicity is a Strategic Advantage
Documentation from Day One — Why Documentation from Day One Matters
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