The formal grammar that constrains the textual form of identifiers in a given scheme — what character sets, lengths, prefixes, separators, and check digits are allowed — typically expressed as a regular expression or BNF grammar in the scheme's specification.

ByCASRAI Editorial Board

· Last updated 10 Jul 2026

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 surface-level part of an identifier scheme. ORCID iDs have a fixed 16-digit pattern with a final ISO-7064 check character. DOIs have a prefix ’10.NNNN’ and a case-insensitive suffix of any Unicode characters. ARKs have ark:/NAAN/Name[Qualifier]. UUIDs have 8-4-4-4-12 hex grouping. Conforming to identifier syntax is a precondition for resolution. Validation libraries on the client side typically check syntax before submission to avoid round-tripping invalid identifiers.

References

Paskin N., 'Digital Object Identifier (DOI) System' in Encyclopedia of Library and Information Sciences, 2010.

Also known as

Identifier format

Machine-readable encodings

Use in your systems

JATS XML <role> element

xml

<role vocab="credit"
      vocab-identifier="https://casrai.org/dictionary/"
      vocab-term="Identifier syntax"
      vocab-term-identifier="https://casrai.org/dictionary/term/identifier-syntax" />

Schema.org DefinedTerm (JSON-LD)

json

{
  "@context": "https://schema.org",
  "@type": "DefinedTerm",
  "@id": "https://casrai.org/dictionary/term/identifier-syntax",
  "name": "Identifier syntax",
  "identifier": "https://casrai.org/dictionary/term/identifier-syntax",
  "description": "The formal grammar that constrains the textual form of identifiers in a given scheme — what character sets, lengths, prefixes, separators, and check digits are allowed — typically expressed as a regular expression or BNF grammar in the scheme's specification.",
  "inDefinedTermSet": "https://casrai.org/dictionary/domain/persistent-identifiers#set",
  "url": "https://casrai.org/dictionary/term/identifier-syntax",
  "sameAs": [
    "Identifier format"
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/",
  "publisher": {
    "@id": "https://casrai.org/#organization"
  },
  "dateModified": "2026-07-10T02:06:20",
  "inLanguage": "en"
}

Referenced across the research world

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