Change Drivers and Assignment

Change drivers are the engine of the whole theory. Everything the Independent Variation Principle prescribes follows from the set of change drivers and the way elements are assigned to them.

1 What a change driver is

A change driver is a discrete, identifiable source of variation that can cause elements to require modification. It is an external condition in the operating domain: when it activates, part of the system must change.

The tax legislation is a change driver. When it changes, every element that embodies tax knowledge must change. A payment-routing standard is a change driver. The target platform is a change driver. A security classification is a change driver.

At the leaf level, a change driver is identical to a coupling dimension: both name a dimension along which elements vary together.

2 Change drivers are discovered, not chosen

This is the load-bearing fact about change drivers. The set $C$ is a fact about the domain, not a design choice. The analyst discovers which external conditions force the system to change; the designer does not invent them.

Change drivers are external and fixed by the domain. No design move adds, removes, or transmutes a driver. A change driver exists because the domain’s causal structure produces it, not because a designer decides it should exist.

This is why the theory is a diagnostic instrument rather than a recipe: it tells you to read the change structure off the domain, not to impose it.

3 The assignment function

The change-driver assignment $\Gamma : E \to \mathcal{P}(C)$ maps each element to the set of change drivers that force it to change.

• An element with $|\Gamma(e)| = 1$ responds to exactly one change driver. Such an element is pure.
• An element with $|\Gamma(e)| > 1$ responds to several. It is composite.
• A composite element is irreducibly composite when no proper subset of its driver set can achieve its purpose — it genuinely needs all of them. Adapters and translators are typical examples: a module that must both follow the domain’s rule and satisfy a foreign interface is irreducibly multi-driver.

The assignment is read from the domain’s causal structure. Whether an element is pure or composite is not a label the designer attaches; it follows from which external conditions actually force the element to change.

4 Driver independence

Two change drivers are independent when their knowledge slices do not overlap and activating one does not logically force the other. Driver independence is a well-formedness condition on the driver set, not a hypothesis the theory requires. If two drivers are mutually coupled — each activation forces the other — they do not individuate two distinct sources of change and are correctly treated as one.

5 Driver omission and refinement

The granularity at which you read the driver set is a modelling choice. You may split one change driver into finer ones, or merge several into one coarser driver. The structural results of the theory are invariant under this refinement: a finer grain yields a richer $C$ with no loss of structural validity.

Omitting a driver — failing to record a genuine source of change — is a different matter. It coarsens the optimal partition and leaves that change uncontained. Driver omission is the failure mode the theory warns against: if a real change driver is missing from $C$, the modules built from the incomplete set will not contain the changes that driver produces.

The taxonomy of change drivers and the discovery tests used here are developed in the published paper on the change-driver taxonomy [1], and the question of what counts as the source of a change driver is examined in the paper on whether a change driver is an actor or a document [2]. The formal account of the assignment function and of driver independence is part of the Independent Variation Principle paper [3].

---

The formal development. The definitions, theorems, and proofs behind this page are published in:

• The Change-Driver Taxonomy — Zenodo, 2026 — doi:10.5281/zenodo.21669704
• Change Driver: Actor or Document? — Zenodo, 2026 — doi:10.5281/zenodo.21669958
• The Independent Variation Principle — Zenodo, 2026 — doi:10.5281/zenodo.20794332

All published papers

References

[1]

Y. Loth, “The change-driver taxonomy.” Zenodo, Jul. 2026. doi: 10.5281/zenodo.21669704.

[2]

Y. Loth, “Change driver: Actor or document?” Zenodo, Jul. 2026. doi: 10.5281/zenodo.21669958.

[3]

Y. Loth, “The independent variation principle.” Zenodo, Jun. 2026. doi: 10.5281/zenodo.20794332.