3 The Selmo method (PTF)

This chapter describes the methodological basis of Selmo.

It is consciously placed before the model core and answers a central question:

How must one think about a machine, before it is modeled?

The Selmo method prevents that:

• modeling is done too early

• technical details dominate the process

• implicit assumptions enter the model

• complexity grows uncontrollably

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Why a method is necessary before the model

A formal model is only as good as the thoughts that led to its creation.

Without upstream methodology the following arise:

• overloaded sequences

• technically driven states

• safety logic as a repair

• hard-to-explain models

Therefore Selmo separates Thinking and Modeling strictly.

Not everything that is technically possible, is also functionally sensible.

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PTF – Process · Technology · Function

The Selmo method is based on three clearly separated levels:

• process What should happen functionally – independent of technology?

• Technology Which physical and technical principles are used?

• Function Which verifiable requirements necessarily result from this?

These three levels together form the PTF structure.

PTF is:

• not a diagram

• not a tool

• not a substitute for engineering

But:

A framework of thought that prepares modeling and limits complexity.

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Role of PTF in the overall structure

The classification is clear:

PTF (Thinking & Analysis) ↓ Selmo model (formal & deterministic) ↓ PLC / HMI / Diagnostics (implementation)

PTF decides:

• what is modeled

• why it is modeled

The Selmo model decides:

• how this behavior is described formally

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Distinction from the model core

This chapter describes no:

• Sequences

• zones

• States

• Bit-Control

• Operating modes

These elements therefore deliberately belong in the following chapters.

PTF:

• creates clarity

• reduces modeling errors

• prevents implicit logic

PTF is the prerequisite for good models – not their replacement.

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Structure of this chapter

Chapter 3 is divided into two parts:

3.1 PTF – Process · Technology · Function

→ the method in detail → thinking model and typical errors

3.2 Digital Twin as behavior model

→ distinction from marketing terms → classification of the Selmo model relative to reality

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Transition to the model core

After this chapter it is clear:

• which questions must be answered before modeling

• which assumptions not belong in the model

• why Selmo models remain lean and explainable

The following chapters describe the formal core of Selmo:

• structure

• Logic

• Behavior

• Operation

• Safety

Think first. Then model. Then automate.