Examples
Worked examples
- Is an instance
'doi' as a scheme value alongside the identifier '10.1038/nature14539' in a metadata record.
- Is an instance
'orcid' as a scheme indicating that the accompanying identifier is an ORCID iD.
Counter-examples
Looks similar, but isn't
- Not an instance
'paper' is not an identifier scheme — it describes the entity type, not the naming system.
- Not an instance
'unique' is not an identifier scheme.
- Not an instance
A single institution's internal accession number, with no external minting authority or resolver, is not a PID scheme in this sense — it is a local database key.
Editorial commentary
Examples of identifier schemes include DOI, Handle, ARK, ORCID, ROR, ISNI, URN, UUID. Each scheme is defined by some combination of standards documents (ISO standards, IETF RFCs, community specifications), governing bodies (DataCite, Crossref, CNRI, ORCID Inc., and similar), and operational infrastructure (registries, resolvers). When a CRIS or repository must record an identifier, declaring ‘which scheme this is’ is essential to interpretation — ‘12345’ alone is meaningless without the scheme.
The four defining properties
A named identifier scheme is generally defined by: (1) a syntax — the rules for a valid identifier string, e.g. DOI’s prefix/suffix format or ORCID’s 16-digit checksum-validated pattern; (2) a minting authority — who is allowed to issue new identifiers, e.g. DataCite/Crossref member organisations for DOIs, ORCID Inc. for ORCID iDs; (3) a metadata schema — what descriptive information must accompany the identifier at registration; and (4) a resolution policy — what technical infrastructure resolves the identifier to a current location, e.g. the Handle System underlying DOI resolution.
Scheme vs. a single identifier vs. syntax
An identifier scheme is not the same as a single instantiated identifier (e.g. “10.1038/nature14539” is one DOI within the DOI scheme, not the scheme itself) and is a broader concept than pure syntax rules alone — syntax describes only how the string is formed, while a scheme also specifies who may mint and how resolution works. In metadata records, a scheme is typically paired explicitly with a value — for example DataCite’s alternateIdentifiers block requires both an alternateIdentifierType (the scheme) and the value, precisely because the bare value is ambiguous without it.
References
- Klump J., Wyborn L., ‘Identifiers for the 21st Century’, Data Science Journal 16(28), 2017.
Also known as
PID scheme
Machine-readable encodings
Use in your systems
<role vocab="credit"
vocab-identifier="https://casrai.org/dictionary/"
vocab-term="Identifier scheme"
vocab-term-identifier="https://casrai.org/dictionary/term/identifier-scheme" />{
"@context": "https://schema.org",
"@type": "DefinedTerm",
"@id": "https://casrai.org/dictionary/term/identifier-scheme",
"name": "Identifier scheme",
"identifier": "https://casrai.org/dictionary/term/identifier-scheme",
"description": "A named, formally-defined system for constructing, issuing, and resolving identifiers, typically defined by a syntax, an authority structure (who can mint), a metadata schema, and a resolution policy.",
"inDefinedTermSet": "https://casrai.org/dictionary/domain/persistent-identifiers#set",
"url": "https://casrai.org/dictionary/term/identifier-scheme",
"alternateName": [
"PID scheme"
],
"license": "https://creativecommons.org/licenses/by/4.0/",
"publisher": {
"@id": "https://casrai.org/#organization"
},
"author": {
"@id": "https://casrai.org/#editorial-team"
},
"datePublished": "2026-05-21T02:12:19",
"dateModified": "2026-09-05T17:30:59",
"inLanguage": "en-GB",
"isAccessibleForFree": true
}
