Citations are important in scholarly publishing. A scholar’s publication record can make or break a career. For better or worse, tenure committees evaluate those publications based on citation measures like Thomson Reuter's Impact Factor, the h-index, or perhaps by emerging article-level metrics showing citations and links to an individual piece of content.

What is Reference Linking

CrossRef makes it possible for a reader of a scholarly journal to click the citations or references of an article and be taken directly to the full text of the article being cited. CrossRef achieves this through the use of Digital Object Identifiers (DOIs), which are persistent links.

Of course citation linking is broader than just linking in journal articles. Few people are aware that of the 48 million items that have CrossRef DOIs, about 7% of them are assigned to books at the chapter level. As a matter of fact, books are the fastest growing content type at CrossRef. Other important content includes proceedings papers, reports, and theses. Even individual figures and tables within a document can have DOIs.

Why Persistence Matters

What exactly do we mean when we say a DOI is a persistent link? The CrossRef member publisher who owns the content and assigns the DOI is making a commitment to that content—to keeping it available indefinitely. But how does that work when publishers buy and sell journal titles, stop publication, transfer hosting platforms, and sometimes even go out of business?

CrossRef works on both a technical and a social level. It manages the actual deposit of DOIs with the Handle System (a third-party technology), and is a Registration Agency of the International DOI Foundation (IDF). The DOI system “resolves” a DOI to the publisher’s website. CrossRef also provides look-up services for DOIs. If you have bibliographic metadata for a piece of content, CrossRef can return the DOI. Conversely, if you have a DOI, it can give you the metadata.

The other, and equally important, part of persistence is a social contract. The publisher
promises to keep the URLs for its content updated at CrossRef. They promise to keep the content up and available. If they buy or sell journal titles, they promise to work with CrossRef and the other publisher to make sure the URLs are updated. They make arrangements with an archiving organization such as CLOCKS, Portico, or a national library so that in the event that they cease publication or go out of business, the DOI can continue to resolve to the archival version of the content.

If a user gets an error message when trying to click on or resolve a DOI, it is most often because the creator of the link made a mistake. Publishers may also erroneously publicize DOIs before they are live, or change URLs without updating them at CrossRef. Publishers who agree to be part of CrossRef must take their commitments seriously, or the value of the persistent link is severely diminished for everyone. CrossRef forwards every broken DOI report to the appropriate publisher for correction.

Luckily for smaller publishers, CrossRef Service Providers, such as Allen Press, are authorized to make DOI deposits (assigning DOIs) and to do queries (discovering DOIs) on behalf of their publisher customers. Because of this, members do not have to manage gnarly XML on their own in order to participate in the reference linking system.

How to Display DOIs

CrossRef has more than 1,000 publisher members and thousands of library affiliates, and the CrossRef reference linking system has been operational for more than 10 years. For the first time since the system went live, CrossRef has just changed its recommendations for how to display CrossRef DOIs in online publications. Effective immediately, the new display guideline is to display the CrossRef DOI as a link. To do this, you just add http://dx.doi.org/ before any DOI. For example, the old format was displayed as doi: 10.5085/jfe.22.1.75. It will now become http://dx.doi.org/10.5085/jfe.22.1.75.

The new guidelines document, with information on the reason for this change, is available at http://www.crossref.org/02publishers/doi_display_guidelines.html.