DOI and Crossref, explained

What a DOI is

A Digital Object Identifier (DOI) is a persistent identifier for an object, most often a journal article. It has two parts separated by a slash: a prefix and a suffix. In the DOI Foundation's own example, 10.1000/182, the prefix is 10.1000 and the suffix is 182. The point of a DOI is that it keeps working when a web address changes: the metadata behind it can be updated while the DOI stays the same, and the DOI system redirects a person or a program to the current location. Resolution is free.

The DOI Foundation makes the point that persistence depends on organisations, not only on technology. A DOI is therefore only as reliable as the publisher who registered it and keeps the record current.

What Crossref does

Crossref is a registration agency. Its members, such as publishers and journals, register their content and deposit metadata records that connect each item to an identifier. Crossref then makes this metadata openly available through APIs in JSON and XML. Members must keep their registered metadata current, including URLs, licences and Crossmark data.

The metadata can include bibliographic details, funding information, licences, post-publication updates such as corrections and retractions, ORCID and ROR identifiers, and abstracts. What is actually present for a given article depends on what the publisher deposited, so empty fields are normal and should not be filled in by guesswork.

Crossref is one DOI registration agency among several. Not every DOI is a Crossref DOI, so a DOI that Crossref cannot find may still be valid with another agency.

Turning a DOI into a reference

A DOI should be shown as a full link in the form https://doi.org/10.xxxx/xxxxx. Crossref's display guidelines advise using HTTPS and the doi.org domain, and not putting "doi:" or "DOI:" in front of the link. Older links that start with dx.doi.org still work, but new references should use the current form.

To get a ready-made citation, you can use content negotiation. A request to the DOI link with an Accept header returns the metadata in the format you ask for. For example, the header application/x-bibtex returns BibTeX, and text/x-bibliography returns a formatted citation when you also pass a style and a locale. Citation styles come from the Citation Style Language repository, and Crossref lists the available styles on its API. Many reference managers do this for you when you paste a DOI.

Always check the result against the article. Automatically generated references can contain wrong capitalisation, missing diacritics (a common problem with Turkish characters) or missing authors. For journals that follow Vancouver style, confirm the format required by the journal you are submitting to.

Checking a DOI

• Click it. Open https://doi.org/ followed by the DOI. It should land on the article page of the publisher, with the same title and authors.
• Look at the record. The Crossref REST API at https://api.crossref.org/works/ followed by the DOI returns the deposited record as JSON. No sign-up is needed. If you automate requests, add your e-mail address in the mailto parameter so you are served by the polite pool.
• Check for updates. The record can include corrections or retractions linked to the article, and the publisher's page may show a Crossmark button.
• Be careful with typos. One wrong character gives another article or no result. Copy and paste instead of retyping.

A DOI shows that an item was registered. It does not show that the work is peer-reviewed or correct, and it does not say anything about the quality of the journal.

Sources

• DOI Foundation, What is a DOI: https://www.doi.org/the-identifier/what-is-a-doi/
• Crossref, principles and practices: https://www.crossref.org/documentation/principles-practices/
• Crossref, DOI display guidelines: https://www.crossref.org/display-guidelines/
• Crossref, REST API: https://www.crossref.org/documentation/retrieve-metadata/rest-api/
• Crossref, content negotiation: https://www.crossref.org/documentation/retrieve-metadata/content-negotiation/
• Crossref, Crossmark: https://www.crossref.org/services/crossmark/