Examples
Worked examples
- Is an instance
ORCID syntax: ^\d{4}-\d{4}-\d{4}-\d{3}[\dX]$.
- Is an instance
DOI syntax: ^10\.\d{4,9}/[-._;()/:A-Za-z0-9]+$.
Counter-examples
Looks similar, but isn't
- Not an instance
A field label such as 'Authors' is not identifier syntax.
- Not an instance
A natural-language description of a paper is not identifier syntax.
Editorial commentary
Identifier syntax is the formal grammar constraining the textual form a valid identifier within a scheme may take — permitted character sets, length, fixed prefixes or delimiters, and any check character used to catch transcription errors — typically expressed in a scheme’s specification as a regular expression or a formal (BNF-style) grammar.
Worked syntax patterns
An ORCID iD has a fixed 16-digit pattern in four groups of four, with the final character an ISO 7064 mod-11-2 checksum digit (which may be the letter X): 0000-000X-XXXX-XXXX. A DOI has a registrant prefix beginning “10.” followed by a registrant code, then a forward slash and a case-insensitive suffix that can technically be any Unicode string the registrant chooses — DOI syntax is deliberately permissive at the suffix level, unlike ORCID’s fixed-format check-digit pattern. An ARK follows the pattern ark:/NAAN/Name[Qualifier], where NAAN is a registered Name Assigning Authority Number. A UUID follows fixed 8-4-4-4-12 hexadecimal grouping regardless of which UUID version generated it. Conforming to the declared syntax is a precondition for resolution to even be attempted — a string that fails an ORCID’s checksum, for instance, is rejected before any lookup happens, which is why client-side validation libraries typically check syntax locally before round-tripping a request to a resolver.
How this differs from “identifier scheme” — a real, deliberate distinction
Identifier syntax is one component nested inside the broader concept of an identifier scheme, not a synonym for it. A scheme is defined by four things together: syntax (the string-format rules covered here), a minting authority (who may issue new identifiers under the scheme), a metadata schema (what descriptive information must accompany registration), and a resolution service (the technical infrastructure that resolves an identifier string to a current location or record). Syntax alone tells you whether a string is well-formed; it says nothing about who was authorised to mint it, what metadata should exist behind it, or how to resolve it. Two identifiers can share syntactically similar formats while belonging to entirely different schemes with different minting authorities — syntax validity is necessary but never sufficient evidence that an identifier is real or currently registered.
Worked example / counter-example
A CRIS system validating a newly entered ORCID iD against the ^d{4}-d{4}-d{4}-d{3}[dX]$ pattern before attempting to resolve it against the ORCID registry is enforcing identifier syntax as a first-pass sanity check. A free-text author-name field, or a project label like “Q3 climate study,” is not identifier syntax at all — it has no defined grammar to validate against, which is exactly the ambiguity a properly-typed PID metadata field is designed to eliminate.
References
- Paskin, N., “Digital Object Identifier (DOI) System,” in Encyclopedia of Library and Information Sciences, 2010.
- ISO 7064 (check-character systems); RFC 8141 (URN syntax).
Also known as
Identifier format
Machine-readable encodings
Use in your systems
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vocab-term="Identifier syntax"
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},
"datePublished": "2026-05-21T02:12:25",
"dateModified": "2026-08-22T16:26:47",
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