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On Identifiers: DOI, ISBN, CASRN, SSN, ISSN, etc.

The views expressed are those of the author and are not necessarily those of Scientific American.

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Over the course of my life I have gone by many names: Ba Ba (early childhood nickname given to me by a younger sister learning to talk), Beege (my grandma calls me this, I’m never quite sure how to spell it), Bonnie, Red (a camp nickname), BONNIE JEAN MULLER (when my parents were angry at me), Bonnie Muller, Bonnie Swoger, etc. Any of these names can refer to me.

But there are also multiple versions of folks with each of these names. There are several Bonnie Swogers or Bonnie Mullers and thousands of Reds and Bonnies in the US alone.

In order to distinguish me from other folks with the same name, you need to look at other factors: location, occupation, physical appearance, etc.

But there is one way the immediately identifies me and keeps me distinct from everyone else with my name: my Social Security number. I have many names, but only one social security number. Conversely, my social security number applies only to me and not to anyone else.

When we start looking at information sources, there are many similar types of identifiers that help us pinpoint the exact item we are talking about while helping to distinguish that item from other similar items.

ISBNs and barcodes of the books on my desk right now.

ISBNs and barcodes of the books on my desk right now.

In libraries, a common identifier is the ISBN, or international standard book number. Go ahead and pick up the book closest to you. Most likely, if you look at the bottom right hand corner of the back cover, you will see a bar code and a series of numbers on top of the bar code preceded by “ISBN:” Each ISBN identifies a particular version of a book. I have three hardcover versions of my favorite book Pride and Prejudice (insert isbn’s here), one paperback version (isbn) and one Kindle version (ISBN). So while the ISBN is extremely useful for identifying a particular version of a book, it isn’t very good at identifying all versions of that book. ISBN were introduced in the 1970s and have revolutionized the way that publishers, booksellers and libraries keep track of their inventories, but they aren’t necessarily helpful when you don’t care which version of Pride and Prejudice you want.

Another identifier used extensively in the scientific literature is the Digital Object Identifier (DOI). A DOI is just like a social security number for a digital item (journal article, data file, presentation file, etc.). Each journal article has a DOI, and no two articles have the same DOI. A DOI normally consists of numbers, letters and other punctuation. It will look like this:



The DOI provides a way to permanently find a particular item. Publishers and scholarly societies change their websites all the time. Recently, a major publisher completely re-did their website, messing up all links into their site. I was quite annoyed. But the DOI could still link you to an article in a way that a URL couldn’t.

The DOI is a great way to identify a particular journal article, but identifiers for journals have been around for some time. The ISSN is an 8 digit number applied to serial publications (magazines, journals, etc.), and can be especially helpful in distinguishing journals with similar names or commonly misspelled names. The ISSN suffers from some of the same challenges with respect to format as the ISBN. Typically, a publication could have two different ISSN numbers: one for a print version and one for an electronic version.

While ISBNs and DOIs apply to information sources across the disciplines, certain disciplines have specific information needs. In chemistry, keeping track of molecular compounds can be quite difficult. Historic names can be regional, obscure or too similar sounding to other terms. Compounds can be made of the same components but built differently. Compounds with similar structures can contain different elements or isotopes. In the mid-20th century, Chemical Abstracts Services, a division of the American Chemical Society, started assigning unique identifying numbers to each compound described in the chemical literature. With a few exceptions, each distinct chemical compound gets a unique CASRN. This help chemists purchase, research and use the exact chemicals they need for their work.

As the amount of information available to us increases exponentially and occasionally feels overwhelming, identifiers become more and more important to help us identify the information we need while filtering out the stuff we don’t. What identifiers do you use or come across regularly?

Bonnie Swoger About the Author: Bonnie J. M. Swoger is a Science and Technology Librarian at a small public undergraduate institution in upstate New York, SUNY Geneseo. She teaches students about the science literature, helps faculty and students with library research questions and leads library assessment efforts. She has a BS in Geology from St. Lawrence University, an MS in Geology from Kent State University and an MLS from the University at Buffalo. She would love to have some free time in which to indulge in hobbies. She blogs at the Undergraduate Science Librarian. Follow on Twitter @bonnieswoger.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Sean McCann 10:11 am 02/7/2013

    I am finding the DOI to be very helpful… I am about to publish a paper with multiple digital media attached, and will have a DOI for the entire collection, which will be hosted at FigShare.

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  2. 2. jtdwyer 8:45 pm 02/7/2013

    It might should be mentioned that the article identified by a doi number (when not encoded as a dynamic link) can be accessed by appending it to “”. Per your examples:

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  3. 3. literarymachine 4:44 am 02/15/2013

    I would argue that the most common identifiers used nowadays are URLs, and that they are here to stay. The possible problem of them not being stable is not inherent to URLs; mapping DOIs to URLs is not more stable “by nature”. Identifier persistence is a matter of best practices and cool URIs don’t change!

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  4. 4. epentz 8:46 am 02/18/2013

    Thanks for a useful summary. With DOIs it’s important to note that there are different DOI agencies with different services – e.g. CrossRef, DataCite and EIDR ( – DOIs for movie and TV) amongst others.

    With respect to URLs CrossRef DOIs are URLs. One problem with the URLs is that domain names aren’t owned, merely leased, and when journals change ownership the domain names of the URLS have to change. With CrossRef DOIs the use of a central resolver – – helps when the underlying URLs change. The URL has to be updated in one location and any links using the DOI automatically go to the correct location. I wholeheartedly agree, though, that persistence is not guaranteed by technology but by people and organizations.

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  5. 5. Bonnie Swoger in reply to Bonnie Swoger 10:27 am 02/19/2013

    Thanks, everyone, for all the additional details about DOIs.

    epentz made the important point that these identifiers are only useful because of the people behind them. The technology makes it possible, but people are necessary to maintain the system.

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