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What Is a DOI number?: Home

What Is a DOI?

The letters DOI stand for Digital Object Identifier, which is an alphanumeric string of characters constructed  to identify uniquely and in a persisting way some digital content. A good analogy would be the Social Security number here in the USA, which is assigned to a person at birth and continues to identify that person uniquely until death.

What Does A DOI Look Like?

A DOI is a string of chraracters. The portions of the string are "significant", in that the various segments convey meaning. A typical DOI looks like this 10.1000/182

a. all DOI strings begin with 10. Strictly speaking, 10. is not part of the DOI string. It is a kind of general identifier proclaiming that what follows is a DOI, as opposed to some other kind of digital identifier.

b. the string is composed of a prefix, which is all charactersafter 10. and before the slashand a suffix with all characters after.

c. in the example above, 1000 denotes the Registering Agency (here, the International DOI Foundation) and 182 is the item id, the DOI Handbook.

d. in practice, Registering Agencies use various methods to specify individual items, including sequential numbers, vol/page combinations, or variations of these. Some publishers supply the letters DOI or doi as an aid to users. Others expect users to realize what 10. means. Here are some examples of the various styles:

          DOI 10.1016/j.leukres.2008.10.006

          DOI 10.1038/sj.neo.7900253

          DOI 10.1111/j.1745-7270.2008.00433.x


          10. 1109/16.8842

Where Do DOIs Come From?

A DOI is assigned by one of the members of the International DOI Foundation (IDF). The IDF is a consortium of companies and agencies which have a strong professional interest in organizing and preserving access to digital content of all types. Membership in the IDF is restricted to those bodies that are in a position to fulfill certain contract obligations and pay membership fees. The fees defer the costs of maintaining the system. The member organizations serve as Registering Agencies, or RAs, and assign DOI tags to individual items, following the IDF's strict protocols. Publishers are one obvious type of organization comprising the IDF. CrossRef, for example, is a consortium of over 3,000 publishers.

Is A DOI Like A URL?

URLs and DOIs are both identifiers, so in that sense they are similar. But a URL is used to denote a place, a site on the web somewhere, at which a particular document can be found. Restructuring a web site can break the previous URL, and the document becomes unavailable.

A DOI is used to identify a document, not a place or site. The DOI will always refer to the same entity no matter where on the web that document is found, because the DOI is "registry based". Metadata, or information about the document such as its title and author, is stored separately in the registry. A query to the registry resolves the DOI, and points the user to document's current location.

Does Every Article Have A DOI?

No, at least not yet. The emphasis by publishers has been on assigning DOI strings to new publications, so it's possible that older articles will not have DOI tagging. And "older" doesn't have to be very old. Some publishers are retro-tagging older material very aggressively, while others are not. If a publisher has digitized large portions of journal backfiles, the odds are good that DOIs were added as part of the process. Still, there is no statement that does not have exceptions, so it's better to check in each case.

If An Article Has A DOI, Where Is It?

The DOI string can usually be found at some location on the first page of an article. Practice varies among publishers, so it's hard to generalize. Many publishers in science, technology or medicine provide brief renditions of the bibliographic particulars (journal, vol, page, year) in a somewhat smaller typeface on the left side of the first page of an article. But, some other publishers may place it at the right or on the bottom of the first page.

Many literature discovery services such as MEDLINE, PsycINFO and CINAHL include the DOI as part of the indexing data for the article. Again, practice varies. PubMed MEDLINE for example has an AID field, and if the article has a DOI it will be found here. But other literature search services may have a dedicated, labeled field for the DOI. Unfortunately, the user must become accustomed to the conventions of each service.

Are DOIs Mandatory In References?

Not at the moment, but a check of some of the major style guides for professional societies or scholarly publication (Chicago Manual of Style, The American Chemical Society, the American Psychological Association) strongly recommend that DOIs be included in article references if they are available. At some time in the future, as more digital content is tagged with DOI strings, it could be that including DOIs in the citation apparatus will become mandatory.

Can I Look Up DOIs?

Yes. Direct and reverse DOI lookups are possible, but on different sites. If you have only the DOI and want the full reference, or even a link to an appropriate copy of the entire text, do this:

a. login to the DOI resolver at:

b. type the DOI onto the query line. If the item has a DOI, the system will determine this and provide a link to whatever version you are allowed to view, based on subscription or other access stipulations.

If you have a citation, and want to determine if it has a DOI:

a. login to the CrossRef system at:

b. fill in the blanks on the search form with all the information you can provide. CrossRef will determine if the item has a DOI and then display it.

How Can I Link To Our Library's Content?

1. The link will have three segments: the UTMB proxy prefix, the DOI resolver address, and the DOI number.

2. Locate the DOI number of the article to which you want to make a link.

3. Use the following character groups for the UTMB proxy prefix and the DOI resolver address respectively;

         http//   AND

4. Add the DOI number to the string immediately after the colon. The final link looks like this:


The DOI system is relatively new, and is a part of a much larger system which plans to provide similar persisting locator information for things other than publications. Publishers and companies or agencies involved in the creation, sale, updating or managing of "publications" very broadly conceived have been enthusiastic users of the DOI methods. Much has been accomplished already, but much still remains undone. There are considerable expenses involved in the assignment of DOI locators, so larger firms and agencies, with greater resources, are better placed to make progress than are smaller ones. But all persons involved in research, teaching, or academic pursuits generally should be aware of the impact DOIs will make and should monitor developments.

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