Updated OpenURL and CrossRef information is now available

What CrossRef is:
A not-for-profit network founded on publisher collaboration, with a mandate to make reference linking throughout online scholarly literature efficient and reliable and develop other services that are best achieved through collaboration. CrossRef is a DOI Registration Agency and is committed to long term sustainability.

What a DOI is:
A unique alphanumeric string assigned to a digital object – in this case, an electronic journal article or a book chapter. In the CrossRef system, each DOI is associated with a set of basic metadata and a URL pointer to the full text, so that it uniquely identifies the content item and provides a persistent link to its location on the internet.

For more information on the DOI itself, which is a NISO standard syntax, please visit the International DOI Foundation website at www.doi.org. For details on use of the DOI within CrossRef, please see the "How CrossRef Works" page.

What CrossRef is not:

• A product for sale
• An article database
• A direct-to-end-user service
• A search interface
• A broker of full-text content
• Made up of just big commercial publishers

CrossRef's mission:
CrossRef is a not-for-profit membership association whose mission is to enable easy identification and use of trustworthy electronic content by promoting the cooperative development and application of a sustainable infrastructure.

Who developed CrossRef?
Scholarly publishers developed CrossRef. The initial service was based on a prototype developed by John Wiley & Sons and Academic Press, in cooperation with the International DOI Foundation (IDF). It built on the DOI-X project led by the IDF, Association of American Publishers (AAP) and the Corporation for National Research Initiatives (CNRI).

Who participates in CrossRef:
Any publisher of primary research material in digital form -- whether large or small, commercial or non-profit, traditional or non-traditional -- can register their content with CrossRef by joining our growing list of members.

A variety of other organizations also participate:

• Libraries use the CrossRef system as part of their localized linking solutions, enriching online catalogues and databases with links to their own full-text holdings where appropriate.
• Intermediaries, including secondary publishers and journal hosting services, use CrossRef as Basic Affiliates and Enhanced Affiliates, enhancing their own products and content offerings with DOI-based citation links.
• Technology companies are creating software tools that interface with CrossRef.

Key benefits of the CrossRef system:

• No broken links: Because a DOI link is a persistent link, unlike a URL, publishers and others who use CrossRef create reliable, persistent links in citations and database records.
• A single agreement with CrossRef serves as a linking agreement with all participating publishers. Avoid having to sign numerous bilateral linking agreements with publishers.
• Add value to your electronic publications: Readers have come to expect online material to contain outbound links to cited sources. At the same time, CrossRef linking will augment the accessibility of your content through inbound links.

How the system works and what publishers have to do:
Publishers of electronic scholarly content join as members and are assigned a DOI prefix. For each content item a publisher wishes to register in the system, it creates a unique DOI (incorporating the assigned prefix) and tags it to the article’s metadata and the URL where the article resides. The publisher submits the record to the CrossRef metadata database (MDDB) in a strict XML-based DTD format. CrossRef then registers each article DOI and URL in a central DOI directory. This allows for permanent inbound links to the publisher’s content, because other publishers, librarians, and affiliates (such as subscription agents and secondary publishers) can retrieve from CrossRef the DOIs that link to that content. For more information on the registration process, see our submission spec.

In a separate process, the publisher also submits the citations contained in each deposited article to the Reference Resolver, the front-end component of the MDDB that allows for the retrieval of DOIs. This way, the publisher can, as part of its electronic production process, add outbound links to any of an article’s citations that point to content already registered in the CrossRef system. The CrossRef website includes technical specifications for querying and a demo of the DOI look-up process. If you know the DOI for an article, that’s all you need to know in order to locate it persistently. If a publisher changes the location of an article, it need only update the URL for the article in one place with CrossRef.

The DOI Resolution system is run by CNRI on behalf of the IDF. When a user clicks on a link containing the DOI, the DOI Resolution system directs the user to the URL submitted by the publisher. The process of resolving a DOI happens outside of CrossRef.

View a flash demo of the system in action.

CrossRef is not an article database:
CrossRef does not aggregate full-text content. Rather, it uses a system of “distributed aggregation” whereby full-text content is linked through a database consisting of minimal publisher metadata. Each record in the database is essentially a triplet: {metadata + URL+DOI}.

Who pays, and how much:

Publishers pay an annual fee based on their publishing revenue, as well as a small transaction fee for each DOI deposit. Please see the publisher fee schedule. Affiliates pay an Annual Administrative Fee, in addition to DOI retrieval fees. Please see the affiliate fee schedule. There is no charge for libraries or researchers to access the system.

Intermediaries participate too:
Intermediaries, such as secondary publishers, aggregators, and abstracting and indexing services, participate as CrossRef Affiliates. Affiliates use CrossRef for DOI retrieval, to link their own records to the location of primary publisher content.

Why libraries participate:
Library users want to navigate directly from citations or database records to journal articles, but library records do not contain article-level information or links. Although CrossRef cannot solve the appropriate-copy problem on its own, because it is not a customizable software product, CrossRef is a key piece of the puzzle in localized linking solutions for digital collections. Library affiliates can use the CrossRef system to look up both DOIs and metadata, which makes all CrossRef publishers OpenURL compliant for the purposes of article-level linking to local holdings. At the same time, libraries who want to expand their users’ access to content not owned will benefit from CrossRef links to the publisher’s full-text source.

Libraries can join either as individual library affiliates or as library consortia.

Interested parties who are not CrossRef members can request an OpenURL account here.

CrossRef does not compete with OpenURL:
OpenURL is a syntax for transporting metadata and identifiers within URLs, and CrossRef is a DOI registration facility. These initiatives complement one another and work together. CrossRef uses the OpenURL syntax in its own system for metadata retrieval and parameter passing, and makes all of its publishers “OpenURL compliant” for its library participants, by allowing them to retrieve publisher metadata from the CrossRef system.

Researchers do not pay for CrossRef linking:
Researchers do not pay for following links enabled by CrossRef. A subscribed user is usually IP-authenticated for direct access to the target article. While that does not mean all users automatically get free access to the full text, the system works to reduce some of the friction in online research by allowing the researcher to navigate at the article level.

How researchers use CrossRef:
A researcher clicking on a CrossRef link will be automatically connected to a page on the publisher's website showing a full bibliographical citation of the article, and, in most cases, the abstract as well. Subscribers are generally authenticated for full text access, and non-subscribed users presented with other options for access (such as subscription, document delivery, or pay-per-view). Researchers in library environments may find that CrossRef links redirect to local holdings.

Technical requirements for participating publishers
Members must do the following in order to participate in the reference linking system:

• Join CrossRef. It is not necessary to get a DOI Prefix before joining CrossRef. The fee for the DOI Prefix is included in the CrossRef Membership Fees and there is no need to pay a separate fee to the International DOI Foundation. After joining CrossRef, information on getting a DOI Prefix and assigning DOIs will be provided.
• Assign DOIs journal articles. It is not necessary to register DOIs separately with the International DOI Foundation since this will be done automatically as part of the CrossRef metadata submission process.
• Adhere to the requirements of the DOI system.
• The publisher must submit a minimal set of metadata about each article as XML compliant with the CrossRef deposit schema: journal title, ISSN, first author, year, volume and issue, page numbers and DOIs and URLs. A publisher may choose to submit additional metadata, at its option. Publishers who have a small volume of records and who cannot easily supply XML can use the Web Deposit Form http://www.crossref.org/webDeposit/ to deposit their metadata.The DOI/URL will be registered with the International DOI Foundation in the DOI Directory.

When metadata is submitted to CrossRef, a publisher must have active Response Pages, i.e. be able to receive incoming links for those articles. This is necessary because when metadata is deposited in CrossRef, other members and users of the system can look up the DOIs immediately and create reference links.

Maintain the accuracy of DOIs and URLs in the DOI resolution system.

Maintain the accuracy of the metadata in CrossRef's metadata database.

Submit reference queries to CrossRef in the defined format. Publishers who have a small volume of references and who cannot easily submit the queries in the defined format may also use the Simple Text Query http://www.crossref.org/SimpleTextQuery/ to look up DOIs to create outbound links in their references. Publishers must incorporate outbound reference links in their current journals in order to participate in CrossRef.

From the article-level metadata that the publisher submits, CrossRef will determine journal-level metadata, including journal titles, title abbreviations (as many variants as possible), ISSNs (online, print, etc.), online start dates (volume, issue, page, cover date), and publisher.

Services and Features currently available at CrossRef:
Other features currently available include multiple resolution, which allows a single DOI to be associated with multiple elements, such as additional URLs, email addresses, pointers to other metadata records, etc.; parameter-passing, which allows a key or some encoded text, such as information about the source of the incoming link, to be sent along with a DOI; and matching of queries, in which every value provided in a query is considered in a weighted manner, adding greater flexibility and accuracy to the DOI matching process.

Cited-by Linking:
Publishers may also participate in Cited-by Linking http://www.crossref.org/citedby.html, an optional service that allows readers to link to materials that cite a publisher's articles. Cited-by Linking allows publishers to incorporate links to citing articles into their online publication platforms. To participate members are required to deposit their references.

CrossCheck
CrossCheck powered by iThenticate (http://www.crossref.org/crosscheck/index.htm) is an initiative started by CrossRef to help its members actively engage in efforts to prevent scholarly and professional plagiarism.

CrossMark
The CrossMark service (http://www.crossref.org/crossmark/index.html) is designed to:

• Communicate that the scholarly publisher is responsible for both the initial publication of a document, as well maintaining any updates to it.
• Enable publishers to advertise the otherwise invisible steps that they have taken to ensure the trustworthiness of their content.
• Highlight important “publication record” information about a document.

FundRef
The FundRef funder identification service (http://www.crossref.org/fundref/index.html) provides a standard way to report funding sources for published scholarly research.

How to join:
Please email info@crossref.org.