10 Standards reference

9.1 Reference to standards

Traceability as a central requirement

This chapter describes, how Selmo addresses normative requirements – not by mapping individual standard items, but by a fundamentally traceable description of machine behavior.

Selmo does not replace a standard. Selmo creates the prerequisite, to meet standards in a robust manner.

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Standards require justification, not code

Key standards in machinery and plant engineering – for example in the area of machine safety and functional safety – share a common thrust:

• Risks must be identified

• Measures must be justified

• Behavior must be described in a traceable way

What is crucial here:

It is not the code that is assessed, but the argumentation behind the behavior.

A working program alone does not provide sufficient evidence for that.

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The structural problem of classical proofs

In classical projects the standards evidence is often:

• distributed across documents

• separated from the control logic

• difficult to link to real behavior

• highly person-dependent

Typical situations:

• Safety assumptions are not explicitly modeled

• Behavior emerges implicitly from code

• Changes break the chain of argumentation

This makes it difficult:

• CE conformity

• auditability

• liability argumentation

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Formal models as an answer to standard requirements

Selmo addresses this problem through a formal behavior model.

A formal model:

• describes states explicitly

• defines permitted and forbidden behavior

• specifies reactions unambiguously

• is independent of implementation details

This makes it traceable:

• why a state exists

• under which conditions it is valid

• which reaction occurs in case of deviation

The model becomes the supporting basis of the argumentation.

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Classification of typical standard requirements

Without citing individual standards, it can be noted:

• Risk consideration → States, conditions and monitors are explicitly modeled

• Functional safety → safety-relevant behavior is formally described and verifiable

• Traceability → Behavior is not implicit, but explainable

• Change control → Changes are made to the model and remain consistent

Selmo thus provides no standard texts, but a structured response to standard requirements.

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Importance for audit and assessment

For audits a Selmo model means:

• Behavior can be demonstrated, not just explained

• States and reactions are unambiguous

• Safety assumptions are traceable

• Deviations are formally justified

Auditors do not have to:

• interpret implicit logic

• “read” code

• reconstruct assumptions

The model speaks for itself.

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Delineation

To clarify:

• Selmo is not a standard

• Selmo does not replace a risk assessment

• Selmo does not replace a safety control

Selmo:

• structures behavior

• makes assumptions explicit

• supports standards-compliant argumentation

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Summary

Standards require:

• traceable behavior

• justified safety measures

• verifiable decisions

Selmo provides:

• a formal behavior model

• explicit states and conditions

• a consistent basis for argumentation

Standards compliance does not begin with the document, but with the model.