adr: add decision record on support for sole trader representation

Documents the consortium's decision to extend the rulebook from "legal
person" to "economic operator" and to leverage EBWOID/EUID-like identifiers
for sole traders. Outcome of the on-site working group session in Amsterdam
(2026-06-11), authored by the AMS Track 4 architecture group.

Author: Alexander Manecke

adr/Support-for-Sole-Trader-Representation.md

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+# Support for Sole Trader Representation
+
+**Authors:**
+
+- Consortium Architecture Working Group AMS Track 4
+
+- Boris Lingl, boris.lingl@datev.de
+- Alexander Manecke, a.manecke@telekom.de
+- Ignacio Ripoll, ignacio.ripoll@corpme.es
+- Iris Speiser, iris.speiser@datev.de
+- Marlene Urbschat, marlene.urbschat@datev.de
+
+## Context
+
+The current PoA/PoR rulebooks focus primarily on legal persons and do not adequately represent sole traders and similar economic actors.
+
+As a result, certain business structures cannot be represented consistently within the current model.
+
+The core trade-off is between maintaining a legal-person-centric model and expanding the scope to support a broader set of economic actors.
+
+## Decision
+
+The consortium will extend the rulebook terminology from "legal person" to the broader concept of an "economic operator."
+
+The consortium will leverage the EBWOID initiative and use an EUID-like identifier approach to support identity representation for sole traders and similar actors.
+
+Where necessary, existing implementations may continue to process legacy terminology during a transition period, provided that semantic interpretation remains aligned with the new rulebook concept.
+
+## Consequences
+
+### What becomes easier?
+
+- Inclusion of sole traders within the ecosystem.
+- Broader applicability of PoA/PoR use cases.
+- Improved alignment with real-world business structures.
+- Better consistency across participating jurisdictions.
+
+### What becomes more difficult?
+
+- Cross-border identifier interoperability remains challenging.
+- National registration systems may use incompatible identifiers.
+- Additional governance may be required for identifier mapping.
+
+### How do we address the risks introduced by this change?
+
+- Reuse existing EBWOID work wherever possible.
+- Define guidance for identifier mapping and interoperability.
+- Continue collaboration with relevant European initiatives addressing economic operator identification.
+- Define a migration approach for legacy terminology to avoid interpretation inconsistencies during rollout.
+
+## Advice
+
+- 2026-06-11: Consortium Working Group: The rulebook should support all relevant economic actors, not only legal persons.
+- 2026-06-11: Identity Domain Experts: Existing EUID-like approaches should be reused where possible.
+- 2026-06-11: Member States: Cross-border identifier harmonization remains an open challenge that requires further work.