Explaining DOIs, ISBNs, ISSNs and Other Publication Identifiers
The modern world is information rich and becoming more so with each passing day. Staggering numbers of new books, articles, reports and other texts as well as audio and visual creations across a wide range of media are produced, shared and published every year, and those numbers are constantly on the rise. The sheer amount of information available to readers necessitates accurate and efficient ways in which to identify and locate individual resources and sometimes even specific parts or elements within those resources. This is certainly the case with the academic and scientific research documents that are published as contributions to the accumulated knowledge in a discipline or field of study and used to inform and support the work of other investigators.
Fortunately, several systems for identifying publications have been designed and implemented, with the numbers and codes they assign to publications proving incredibly helpful for authors, publishers, editors, reviewers, researchers, readers and other individuals who manufacture, advertise, distribute, sell or make use of those publications. Unfortunately, the numbers and codes assigned to identify publications can also be incredibly confusing, and a basic understanding is necessary to benefit fully from the ease and precision they offer. The following list provides definitions and explanations of the most common publication identifiers used for the kinds of items that academics and scientists are most likely to create and consult. The list is not exhaustive, however, and does not cover all of the systems it mentions in equal detail, but it should provide the information many researchers require and is an excellent starting place for further investigation into the various publication identifiers now in use.
ISBN is the initialism for International Standard Book Number. A unique ISBN is normally assigned by the International ISBN Agency and its network of national agencies to each published version or edition of a book, so the hardcover, paperback and electronic versions of a particular book will each be assigned a different ISBN. If there are also different electronic versions of the book, such as an EPUB, a MOBI and a PDF version, each of those will have a different ISBN as well. Even a change in usage rights when all else about a book’s version and format remains the same means the assignment of a new ISBN, but a simple reprint of a previous version or edition of a book does not require a new ISBN. A multi-volume publication may have an ISBN for each volume and another for the set as a whole.
Publishers ordinarily obtain groups of ISBNS to assign to their publications, but independently published books may not have ISBNs at all, although they frequently do. If a printed book has an assigned ISBN, it normally appears in the bottom right corner of the back cover, usually along with the barcode which is itself a form of the ISBN that is scanned in bookstores or other shops when the book is purchased. The ISBN may also or alternatively appear inside the book on the page dedicated to publication and copyright information, and that is a common place to find it in e-books as well. For an audio book provided via a CD-Rom, DVD or other physical medium, the ISBN can appear on the disk label or the packaging, but often does not. ISBNs are frequently included in the metadata and product descriptions of books posted by publishers and booksellers.
Each ISBN now consists of thirteen digits beginning with ‘978’ or ‘979,’ but 10-digit ISBNs were assigned prior to 2007 and are still valid today. A 13-digit ISBN has five parts:
1. The prefix, which is either ‘978’ or ‘979’
2. The registration group indicating the country, language-sharing group of countries or territory where the book was published
3. The registrant, who is usually also the publisher of the book
4. The publication, which is the book or title itself
5. The check digit to enable the detection of common transcription errors
A 10-digit ISBN lacks the initial prefix and uses a different mathematical formula for calculating the check digit, which may appear as an ‘X’ (the Roman numeral for ‘10’).
Both kinds of ISBNs can be separated into their individual parts using hyphens or spaces, but accurate separation is often tricky because most of the parts do not use a fixed number of digits. Even the digits representing a particular publisher or other specific element may not remain consistent in all ISBNs associated with that publisher or element. The initialism ISBN appears before the number for clarity, as in this 13-digit example for a novel – ISBN 9781533573940 – and this applies to electronic books as well, with the use of the term e-ISBN or eISBN proving confusing and best avoided. An ISBN-A, on the other hand, is an actionable ISBN for use in the DOI (or Digital Object Identifier) system.
ISSN abbreviates International Standard Serial Number. ISSNs are unique numbers assigned to serial publications such as scholarly journals and periodicals, newspapers and magazines, annual conference proceedings and reports, directories and lists, databases and collections, and even websites and blogs as well as other continuing publications. The ISSN International Centre uses a network of national centres to assign ISSNs, which in some countries may be required for all serial publications subject to legal deposit. The ISSN can appear on the cover of a printed volume or issue of a journal, ideally in the upper right corner, and can also be encoded into a barcode with additional digits to indicate the issue or volume number. Alternatively, the ISSN can be included with the publication and editorial information on an inside page.
For electronic publications, ISSNs should appear on the homepage or main menu of online serial publications or on the DVD, CD-Rom, microfiche or packaging if the electronic version is provided via a physical medium. As with ISBNs, different means of publication require different ISSNs, so if a journal is published in print, on CD-Rom and online, each will bear a different ISSN, but the same ISSN can apply to different electronic file formats such as the HTML and PDF versions of the same serial. Since the ISSN of a periodical is based on its title and contains no information about the publisher or location, a new ISSN must be obtained when a journal’s title is changed. It is possible for an issue or volume of a serial publication to have both an ISBN as a separate book and an ISSN as part of the serial resource as a whole.
Unlike the ISBN system, the ISSN system makes a distinction between ISSNs for print and those for electronic media, so a print ISSN or p-ISSN applies to a printed serial, whereas an electronic ISSN or e-ISSN applies to an electronic one. In addition, a linking ISSN or ISSN-L is assigned to every serial publication registered in the ISSN system and serves to link all the ISSNs associated with a specific serial across all publication media. The ISSN-L for a journal is generally the same as the ISSN for the first published medium, but if print and electronic versions are published simultaneously, the print version’s ISSN will usually be the ISSN-L. An ISSN consists of eight digits, the last of which is the check digit that is used for detecting errors and can appear as an ‘X’ if the result is ‘10.’ The ISSN number is divided by a hyphen into two groups of four digits. For example, the ISSN for the online version of the journal Nature appears on the About the Journal page of the website as ISSN 1476-4687.
A DOI is a Digital Object Identifier, which does exactly what its name implies – it identi
fies a digital object. DOIs are particularly common for scientific and academic journal articles, but they are also used for identifying many other kinds of documents and materials such as research reports and presentations, data files and data sets, official or government publications, book chapters, audio and video items, images and performances, software and more. DOIs might even be assigned at several levels of a single publication, so a DOI could be associated with a journal title, another with a specific issue of that journal, yet another with an individual article within the issue and still another with a single section or table within the article.
A DOI for any given object is not only unique, but also resolvable, which means that each DOI will resolve to some form of access to the object it identifies, taking the user to an internet location where the object, part of the object or metadata about the object can be found. Each DOI is also persistent, which means that it will always identify the same object and will never change, even when the object’s metadata changes or the object itself is moved and becomes associated with a different website, webpage or Uniform Resource Locator (URL), making it a more stable identifier than a URL as long as the metadata associated with the DOI is current. DOIs can, however, lead readers to versions of documents behind paywalls even though there are free versions available elsewhere, so some DOI resolvers have been developed to favour open-access venues and free versions of the objects identified by searching for them first.
The International DOI Foundation is responsible for DOIs and manages a number of DOI registration agencies that provide services for those who wish to receive and register DOI names or handles. Although there is no set number of characters for DOIs, each DOI consists of a prefix and a suffix separated by a forward slash. The suffix is assigned and begins with the numeral ‘10,’ which distinguishes the character string as part of the DOI namespace; it continues with a full stop (or period) and then a series of four numbers or more (possibly divided by additional stops) that identify the registrant, who is usually the publisher, author or creator of the digital object. The suffix, on the other hand, can consist of numbers and letters, is chosen by the registrant, often includes the relevant ISSN or ISBN, and functions to identify the specific object associated with the DOI.
According to the International DOI Foundation, DOIs should take the form of this example for a journal article – doi:10.1017/S0362152900011995 – but Crossref, one of the main DOI registration agencies, recommends using an entire URL, which would take this form for the same article: https://doi.org/10.1017/S0362152900011995. As a persistent URL (or PURL), this will reliably and permanently redirect users to the correct web location. The DOI for a journal article can usually be found on the first page of the article or along with other metadata for the paper on the journal’s website, and the appropriate DOIs are frequently included in the complete bibliographical references provided for cited sources in academic and scientific publications.
SICI is the abbreviated form for Serial Item and Contribution Identifier. Created by the Serials Industry Systems Advisory Committee, SICIs are variable-length codes used as extensions of the ISSNs that apply to entire serial publications. SICIs enable the identification of specific parts of a journal or other periodical, such as particular issues or volumes, tables of contents and individual articles and abstracts. A SICI code contains three parts and kinds of information. The first is about the item, including the ISSN for the journal or other serial, the date of publication such as month and year (this information is enclosed in parentheses), and the volume and issue numbers. The second concerns the contribution, including the location where the specific contribution begins (such as a page number), the title code derived from the title of the article often as an initialism, and the symbols ‘<’ and ‘>’ which enclose the contribution part. The third is the control segment, including identifiers for the type of SICI, the part of the publication referred to by the SICI (such as an abstract), the format of the content (such as text), the version number and finally the check character for detecting errors. SICI codes can be used to identify a specific resource in the suffix of a DOI, but the colons (:) that often appear in SICI codes (between volume and issue numbers, for example) have proven problematic, and Crossref will no longer register DOIs that contain colons. SICIs are also used in Uniform Resource Names (URNs).
BICI stands for Book Item and Component Identifier, which is a draft standard of the American National Information Standards Organization. The aim is to provide unique codes for specific items within books or similar publications. Just as a SICI code is an extension of the ISSN for a journal or other serial, so the variable-length BICI code would be an extension of the ISBN for a book and would have a three-part structure similar to a SICI with information dedicated to the item, the type of component and the code itself.
PII is the short form for Publisher Item Identifier, which refers to a unique code of seventeen characters that is used by scientific journal publishers to identify individual documents within their publications. PIIs can identify many different kinds of published items, but they are specifically designed to identify items such as articles and chapters within larger types of publications such as journals and books. A PII therefore incorporates the ISSN or ISBN for the larger publication and adds characters to identify the type of source publication as well as the particular item. The 17-character alphanumeric string begins with a character to identify the source publication type – ‘S’ for serials and ‘B’ for books – which is followed by the 8-digit ISSN for serials or the 10-digit ISBN for books. Two characters then specify the year in which the PII was assigned, but only for serials; omitting it from the code for books eliminates the discrepancy between the 8-digit ISSN and the 10-digit ISBN in the final character count of the PII. The next four characters are the item number assigned by the publisher, and the final element is the check digit. When written for human eyes, PIIs can be rendered more legible by adding punctuation such as hyphens, parentheses and slashes at strategic points.
According to the International ISTC Agency, an ISTC or International Standard Text Code is a unique identifier for ‘text-based works,’ with ‘text-based works’ defined as ‘any content appearing in conventional printed books, audio-books, static e-books or enhanced digital books,’ as well as newspapers and journals. Useful for publishing, indexing, cataloguing and marketing, ISTCs are helpful for clarifying matters when the same content appears with different titles or different content shares the same title. An ISTC is made up of sixteen hexadecimal digits, which means that it uses the numbers ‘1’ to ‘9’ and the letters ‘A’ to ‘F.’ The first three characters constitute the registration element used by the agency; the next four represent the year of registration for the ISTC; the next eight represent the specific textual work; and the final place is occupied by the check digit used for minimizing errors. When displayed an ISTC should begin with the initialism ISTC and be separated into its four elements with hyphens or spaces, as in the example provided by the ISTC Agency: ISTC 0A9-2002-12B4A105-7.
ETTN is the abbreviated form of Electronic Textbook Track Number, which is a unique code for identifying electronic books, conference proceedings and journals. Only electronic text files can use this 13-digit numeric code, which is generated on request by Magnanimitas Assn and consists of five parts: three digits to indicate the focus of the text, two digits for the year in which the ETTN was generated for the text, five digits to identify the text itself, two digits for the month in which the ETTN was generated and one check digit for detecting errors.
SBN or Standard Book Numbering refers to the book identifier system that preceded ISBNs in the 1960s. An SBN consists of nine digits instead of the ten digits used by the first ISBNs, but a zero can be added to the beginning of an SBN to produce a valid 10-digit ISBN. This zero does not alter the check digit of the SBN, so no recalculation is needed to transform a 9-digit SBN into a 10-digit ISBN.
An ASIN is an Amazon Standard Identification Number that uniquely identifies individual products, including books and other documents, within Amazon online marketplaces. ASINs consist of ten characters, including letters as well as numerals (B01DUV1T00, for example), and can be found among the product details on the Amazon pages where books are described. The ASIN and the ISBN are the same for a printed book that has a 10-digit ISBN, but the Kindle (MOBI) editions of books do not use ISBNs, so new ASINs are assigned to them when they are published and offered for sale via Amazon marketplaces.
The ISMN or International Standard Music Number is a code for identifying notated music that is published as scores or sheet music in print, online and in all other formats. As with ISBNs for books, a different ISMN is assigned to each version or edition of a musical work or to each part of a musical work that is distributed separately. ISMNs are also similar to ISBNs in taking two different forms. They were originally alphanumeric, beginning with the letter ‘M,’ generally followed by digits to identify the publisher, digits to identify the work and a check digit, with the code as a whole consisting of ten characters. Since 2008, however, ISMNs have had thirteen digits, replacing the ‘M’ with ‘979-0,’ which is followed by blocks of numbers to identify the publisher and the item before the final check digit. The country of publication is not identified in an ISMN as it is in an ISBN, but a single publication can have both an ISBN and an ISMN.
The International Standard Recording Code (ISRC) is used to identify specific recordings in a unique and permanent manner that remains fixed regardless of where, when and how those recordings are used across media and borders. Different recordings, remixes, editions and versions of the same musical work should therefore bear different ISRCs. An ISRC consists of twelve characters, including both numerals and letters, and should be preceded by the ISRC initialism for clarity. The first two characters are the country code and are issued by the ISRC agency, as are the next three characters, which represent the registrant code. The last two digits of the year in which the ISRC is assigned are then provided by the registrant, as are the final five digits, which constitute a unique code allocated by the registrant and must not be repeated within a calendar year.
The ISWC or International Standard Musical Work Code uniquely identifies musical works. An ISWC identifies a specific work, not an individual publication or edition of the work as the ISMN does and not a particular recording of the work as the ISRC does. Each ISWC consists of a prefix character, which so far has always been the letter ‘T’ for musical works, followed by nine digits identifying the specific work and a check digit for detecting transcription errors. The codes are issued sequentially, so they contain no information about the musicians, publishers or places of publication. When displayed, an ISWC often appears with the initial prefix and final check digit separated by hyphens from the rest of the code and full stops (periods) to break the nine digits in the middle into three groups of three, but the punctuation is not required.
An ISAN is an International Standard Audiovisual Number. Administered by the ISAN International Agency and its regional registration agencies, the ISAN system is designed to provide unique and persistent codes to identify audiovisual works such as films, television programmes, advertisements, video games, sports events, newscasts and more. An ISAN is permanently assigned to an audiovisual work, not simply to a particular publication or release, so it enables the identification of any and all versions and manifestations of a specific audiovisual work across a variety of physical and digital media. This is the case even when the title or another aspect of the work changes, so a single ISAN might be linked to an entire film as initially released, versions of the film available in different countries and languages, director and theatre cuts, soundtracks, DVDs and their packaging, clips and trailers, as well as other promotional material. ISAN codes tend to be very long, but they are generally preceded by ‘ISAN’ and divided by hyphens for ease of reading and transcription.
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