Extended level certification (trustworthy…

Extended level certification (trustworthy repository)

The middle tier of a three-level trust framework for research-data repositories, positioned above core level (CoreTrustSeal, a peer-reviewed self-assessment against 16 requirements) and below formal level (ISO 16363, a full external audit). A repository holds extended level certification when it has been awarded the nestor Seal for Trustworthy Digital Archives — a plausibility-checked self-assessment against the 34 criteria of the German standard DIN 31644, administered by the nestor competence network at the Deutsche Nationalbibliothek. It is more rigorous than a core-level self-assessment (more criteria, external plausibility review of the evidence submitted) but, unlike formal level, does not involve an accredited external auditor conducting an on-site or fully independent audit.

ByCASRAI Editorial Board (auto-drafted, pending review)

· Last updated 10 Jul 2026

Worked examples

Is an instance

A national or disciplinary archive that has already achieved CoreTrustSeal (core level) applies separately for the nestor Seal, submitting evidence against DIN 31644's 34 criteria across organisational framework, object management, and infrastructure/security, without yet pursuing a full ISO 16363 audit.

Is an instance

The nestor Seal for Trustworthy Digital Archives itself — awarded by Germany's nestor competence network after a plausibility-checked self-assessment, typically completed in around three months — is the concrete, currently-operating instance of extended level certification.

Looks similar, but isn't

Not an instance

Holding CoreTrustSeal alone is core level, not extended level — CoreTrustSeal's 16 requirements and lighter peer-review process are a different, less demanding tier than the nestor Seal's 34 DIN 31644 criteria.

Not an instance

An ISO 16363 certification is formal level, not extended level — it requires assessment by an accredited external auditor against a much larger evidence-based framework, rather than a repository's own (even if plausibility-checked) self-assessment.

Extended level certification is the middle tier of the widely-cited three-tier framework for assessing whether a data repository is trustworthy, sitting between CoreTrustSeal‘s core level and a full ISO 16363 audit. In practice, extended level is delivered by the nestor Seal for Trustworthy Digital Archives, based on the German standard DIN 31644 (“Criteria for trustworthy digital archives”) and administered by the nestor competence network, hosted at the Deutsche Nationalbibliothek (German National Library).

Where core level certification (CoreTrustSeal) is a lightweight, peer-reviewed self-assessment against 16 published requirements, extended level is a more demanding plausibility-checked self-assessment against 34 DIN 31644 criteria, organised into three areas: organisational framework, management of intellectual entities and their representations, and infrastructure and security. It is still self-directed by the repository rather than conducted by an accredited external auditor — that step up in rigor is reserved for formal level (ISO 16363).

References

nestor (Kompetenznetzwerk Langzeitarchivierung), ‘nestor Seal for Trustworthy Digital Archives’, based on DIN 31644:2012, langzeitarchivierung.de.
Digital Preservation Coalition, ‘Audit and Certification’, Digital Preservation Handbook, dpconline.org.
CoreTrustSeal Foundation, materials describing the tiered core/extended/formal certification landscape, coretrustseal.org.

Use in your systems

JATS XML <role> element

xml

<role vocab="credit"
      vocab-identifier="https://casrai.org/dictionary/"
      vocab-term="Extended level certification (trustworthy repository)"
      vocab-term-identifier="https://casrai.org/dictionary/term/extended-level-certification-trustworthy-repository" />

Schema.org DefinedTerm (JSON-LD)

json

{
  "@context": "https://schema.org",
  "@type": "DefinedTerm",
  "@id": "https://casrai.org/dictionary/term/extended-level-certification-trustworthy-repository",
  "name": "Extended level certification (trustworthy repository)",
  "identifier": "https://casrai.org/dictionary/term/extended-level-certification-trustworthy-repository",
  "description": "The middle tier of a three-level trust framework for research-data repositories, positioned above core level (CoreTrustSeal, a peer-reviewed self-assessment against 16 requirements) and below formal level (ISO 16363, a full external audit). A repository holds extended level certification when it has been awarded the nestor Seal for Trustworthy Digital Archives — a plausibility-checked self-assessment against the 34 criteria of the German standard DIN 31644, administered by the nestor competence network at the Deutsche Nationalbibliothek. It is more rigorous than a core-level self-assessment (more criteria, external plausibility review of the evidence submitted) but, unlike formal level, does not involve an accredited external auditor conducting an on-site or fully independent audit.",
  "inDefinedTermSet": "https://casrai.org/dictionary/domain/data-infrastructure#set",
  "url": "https://casrai.org/dictionary/term/extended-level-certification-trustworthy-repository",
  "sameAs": [
    "nestor Seal",
    "DIN 31644 certification",
    "Extended-level trust certification"
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/",
  "publisher": {
    "@id": "https://casrai.org/#organization"
  },
  "dateModified": "2026-07-10T02:55:06",
  "inLanguage": "en"
}