Monthly Archives: November 2011

A Primer on Digital Object Identifiers

by Carol Anne Meyer of CrossRef in conversation with Erich Van Rijn, University of California Press

As the first installment in my series on digital standards for the Digest, I asked Carol Anne Meyer, the Director of Business Development and Marketing for CrossRef , to answer a few questions about digital object identifiers.  With several ebook initiatives going live that are geared specifically toward the delivery of content that is accessed through academic libraries, it is critical to apply a standards-based approach to the stable identification of digital book content to enable increased discoverability and usage.  This piece is intended to give AAUP members (and others) a basic overview of the DOI, and I encourage those who are interested in a deeper dive into the topic of DOIs to take a look at some of CrossRef’s recorded webinars.

1) Simply put what is a DOI and what purpose does it serve?

CM: A DOI is a Digital Object Identifier. It serves as a unique and persistent identifier or address for digital content on the web. DOIs remain the same even if the underlying address or URL for the content changes. The primary purpose that DOIs serve for scholarly content is to enable reference linking so that readers can click from the references of a scholarly monograph, article, or reference work directly to the content being referenced. DOIs also support services like Cited-By Linking, where users can see other relevant content that cites a particular work. Many book publishers are increasingly concerned about the discoverability of their content. DOIs can increase traffic to book content through reference citations, through secondary databases, and increasingly through third party discovery tools that use CrossRef metadata.

2) What is CrossRef’s role in the assignment and maintenance of DOIs, and what are the first steps publishers should take in setting up a relationship with CrossRef?

CM: The International DOI Foundation (IDF) appoints registration agencies (RAs) to assign DOIs. CrossRef is the oldest and largest IDF RA. About 94% of all the DOIs that have been assigned have come through CrossRef. CrossRef DOIs are DOIs assigned to scholarly publications:  books, book chapters, reference entries, journal articles, conference proceedings, reports, theses, data sets, and even components like individual tables or graphics.

CrossRef maintains a web service that publishers use to deposit bibliographic metadata, including the URL and the DOI of their content. CrossRef works with the handle infrastructure at the Corporation for National Research Initiatives (CNRI) to make the DOI live, which means that a user clicking on a DOI link is redirected to the URL deposited at CrossRef. CrossRef publishers promise to update their metadata if it changes so that any existing references to the DOI still work even if the URL changes.

CrossRef also provides lookup services so that publishers and affiliated organizations can put CrossRef DOI links into their services and tools. These links increase traffic to the member publishers’ content.

Publishers and affiliates add DOI links to the references in their content by submitting metadata queries to the CrossRef system. They get back the DOI that they can use to link to the content of that reference.

CrossRef is a not-for-profit trade association of publishers. In order to participate in the CrossRef DOI system, publishers need to become members of the association. This entails signing a membership agreement and paying an annual fee based on publishing revenue. The membership agreement lists the obligations of all CrossRef members. CrossRef is not just a technical linking solution, it is also a social contract among publishers, and that is why it works.

 3) Does a DOI differ from a URL, and if so, how?

CM: Yes. A DOI redirects users to the URL where content lives on the web. DOIs are designed to be persistent. Imagine that you are a book publisher, and you decide to host your book content directly on your own web site. The full text of each book has its own URL. This is fine. But then in a few years, you decide that the web site you created is starting to look a little dated, and you choose to migrate all of your content to a newly-formed multi-publisher consortium of ebooks, and you want to shut down your old content site. If you participate in the CrossRef DOI system, you would not have disseminated the actual URLs of your content publically; instead, people would use CrossRef DOIs as the web address. So you can move your content to JSTOR, or Project Muse, or Cambridge University Press, or Oxford University Press, or Highwire or some other hosting platform. As long as you update the new URL at CrossRef, everybody who ever had the DOI for the content can still access that same content without getting a URL not found error message.

You may see DOIs expressed in the form “doi:10.xxxx/kjlkjljlj’ on the web. We have recently revised our CrossRef DOI display guidelines to encourage people to always display CrossRef DOIs as URLs, for example in the form “” We have made this change so that people who may not know what DOIs are can still use them by just clicking on the link, or right clicking to copy the link.  The change also makes it easy for machines to recognizes a DOI and to access services like linked data available through CrossRef. And displaying DOIs in the http:/ URL format will also ensure that they work on web-aware mobile devices.

4) Can a DOI be assigned to content that’s hosted on more than one platform?  If so, how does that work?

CM: Yes. CrossRef supports Multiple Resolution for CrossRef DOIs. The publisher works with our technical staff to create an interim page that pops up when a user clicks a link. That interim page gives the user the choice of platforms to access the data.

Another solution that helps users find the appropriate copy of a document hosted in multiple places is library link resolvers. Both Serials Solutions and ExLibris are CrossRef Service providers, and they use CrossRef DOIs to direct users of their systems to the local copy of the content based on a library’s holdings.

5) Should a publisher assign and deposit DOIs themselves, or should they utilize a service provider to assign DOIs on their behalf?  Are there pros and cons to letting someone else assign and deposit your DOIs?

CM: The answer depends on the technical expertise and resources available to the publisher. For significant volumes of content, publishers interact with the CrossRef system through batch XML file transfers. We have found that for some smaller publishers, this can be a burden. CrossRef does have more manual tools such as our Web Deposit Form, Guest Query, and Simple Text Query forms. This requires that somebody sit at the form and copy and paste data to and from the tool.

If this is all too much, publishers may choose to work with a Sponsoring Publisher (this is a member of CrossRef that is also authorized to deposit and query on behalf of other publishers) or a CrossRef Service Provider (a vendor that provides CrossRef services to publishers). The advantage to working with one of these organizations is that they have experience in working with CrossRef and they understand the guidelines and obligations. That expertise may come at a cost, so publishers will have to weigh the cost and benefits of doing it themselves against that of using a third party. We have many publishers using both approaches that are happy with their arrangements.

6) How are DOIs used by the research community?  What is the role of the DOI in bibliographic citations?

CM: The most basic use of CrossRef DOIs by researchers is to click on them and be directed to the content they represent. An increasing number of authors, based on recommendations from the major style guides, are including DOIs in their citation lists, in order to help with accurate production, and ultimately to ensure readers can find the referenced content.

Some more innovative uses are also emerging. The Public Library of Science (PLoS) relies heavily on CrossRef DOIs to generate their Article Level Metrics. Secondary database include CrossRef DOIs in their citation records to enable links to the full text. Paper and citation management services like Talis, Mendeley, EasyBib and PubGet use CrossRef DOIs to help researchers located and link to relevant information.

Next year, CrossRef will roll out a service called CrossMark which will use the CrossRef DOI to help researchers discover if updates have been made to an item of scholalry content and where to find information about such an update.

7) What have the challenges been in maintaining the DOI standard over the last few years, and are there any aspects of the standard that are evolving that presses should be aware of? 

CM: The DOI has been a National Information Standards Organization (NISO) standard for many years, and more recently has been approved as an International Standards Organization (ISO) standard. These standards have been very stable.

As I mentioned, CrossRef has recently changed its display guidelines. This recommendation has been the first change of this nature in the history of CrossRef’s existence. We anticipate that it will take CrossRef members and affiliates some time to change their systems to support this new recommendation, and we plan to work closely with the style guides so that they too can update their recommended citation formats to be consistent with these guidelines.

The biggest challenge to the success of the CrossRef DOI system is probably the compliance of the individual publisher members. Most of the 50 million CrossRef DOIs are stable and direct as they should, due to the cooperation of the publishers who own the content. Our challenge now is to provide better support to smaller and less technically savvy publishers to ensure that every CrossRef DOI remains stable and useful.

8) Do you have any advice for book people who are just getting started?

CM: Remember that metadata is marketing. Laura Dawson of Firebrand Technologies, and a book metadata expert, recently compared good metadata with dental floss. It isn’t romantic, she said, but it makes everything work. Scholarly book metadata should include CrossRef DOIs at the title level, the chapter level, and the reference entry level to improve its importance and visibility in the scholarly communications environment. Services such as the recently announced Book Citation Index from Thomson Reuters make it clear that the better the metadata, the more accessible the content. This is true now, and it will become even more important in the future.