This document provides an overview of identifiers [and their standards and register(s)] relevant for the design of blockchain systems and the interoperability of those systems with non-blockchain systems.

The following criteria were used for inclusion of identifiers in this document:

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Identifiers (and their standards and registers) issued by the public sector for subjects and objects such as citizen numbers, business registration numbers or land registration numbers;

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Identifiers that are internationally recognized and fulfil one of the following criteria:

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An identifier is an international standard of an SDO (Standard Development Organization);

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An identifier is a de facto standard according to the norms of the industry involved (even if it is not an international standard of an SDO).

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Identifiers that have relevance for DLT systems as it fulfils one of the following criteria:

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An identifier that has been used without DLT, but has proven to solve the problems of DLT services using DLT;

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An identifier that was designed with the usage of DLT in mind from the beginning.