# International Standard Serial Number

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Acronym an ISSN, 2049-3630, as represented by an EAN-13 bar code. ISSN-615-682536 ISSN International Centre 1976; 45 years ago > 2,000,000 8 Weighted sum 2049-3630 www.issn.org
ISSN encoded in an EAN-13 barcode with sequence variant 0 and issue number615-682536;
Example of an ISSN encoded in an EAN-13 barcode, with explanation.
ISSN-615-682536 expanded with sequence variant 0 to a GTIN-13 and encoded in an EAN-13 barcode with an EAN-2 add-on designating issue number 13

An International Standard Serial Number (ISSN) is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine.[1] The ISSN is especially helpful in distinguishing between serials with the same title. ISSNs is used in ordering, cataloging, interlibrary loans, and other practices in connection with serial literature.[2]

The ISSN system was first drafted as an International Organization for Standardization (ISO) international standard in 1971 and published as ISO 3297 in 1975.[3] ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard.

When a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in print and electronic media. The ISSN system refers to these types as print ISSN (p-ISSN) and electronic ISSN (e-ISSN), respectively.[4] Consequently, as defined in ISO 3297:2007, every serial in the ISSN system is also assigned a linking ISSN (ISSN-L), typically the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.[5]

## Code format

The format of the ISSN is an eight-digit code, divided by a hyphen into two four-digit numbers.[1] As an integer number, it can be represented by the first seven digits.[6] The last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code (also named "ISSN structure" or "ISSN syntax") can be expressed as follows:[7]

NNNN-NNNC
where N is in the set {0,1,2,...,9}, a digit character, and C is in {0,1,2,...,9,X};

or by a Perl Compatible Regular Expressions (PCRE) regular expression:[8]

^[0-9]{4}-[0-9]{3}[0-9xX]\$.

The ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, that is C=5. To calculate the check digit, the following algorithm may be used:

Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, and 2, respectively:
${\displaystyle 0\cdot 8+3\cdot 7+7\cdot 6+8\cdot 5+5\cdot 4+9\cdot 3+5\cdot 2}$
${\displaystyle =0+21+42+40+20+27+10}$
${\displaystyle =160}$
The modulus 11 of this sum is then calculated; divide the sum by 11 and determine the remainder:
${\displaystyle {\frac {160}{11}}=14{\mbox{ remainder }}6=14+{\frac {6}{11}}}$
If there is no remainder the check digit is 0, otherwise the remainder value is subtracted from 11 to give the check digit:
${\displaystyle 11-6=5}$
5 is the check digit, C.
For calculations, an upper case X in the check digit position indicates a check digit of 10 (like a Roman ten).

To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right (if the check digit is X, then add 10 to the sum). The modulus 11 of the sum must be 0. There is an online ISSN checker that can validate an ISSN, based on the above algorithm.[9]

### In EANs

ISSNs can be encoded in EAN-13 bar codes with a 977 "country code" (compare the 978 country code ("bookland") for ISBNs), followed by the 7 main digits of the ISSN (the check digit is not included), followed by 2 publisher-defined digits, followed by the EAN check digit (which need not match the ISSN check digit).[10]

## Code assignment, maintenance and look-up

ISSN codes are assigned by a network of ISSN National Centres, usually located at national libraries and coordinated by the ISSN International Centre based in Paris. The International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government.

ISSN-L is a unique identifier for all versions of the serial containing the same content across different media. As defined by ISO 3297:2007, the "linking ISSN (ISSN-L)" provides a mechanism for collocation or linking among the different media versions of the same continuing resource. The ISSN-L is one of a serial's existing ISSNs, so does not change the use or assignment of "ordinary" ISSNs;[11] it is based on the ISSN of the first published medium version of the publication. If the print and online versions of the publication are published at the same time, the ISSN of the print version is chosen as the basis of the ISSN-L.

With ISSN-L is possible to designate one single ISSN for all those media versions of the title. The use of ISSN-L facilitates search, retrieval and delivery across all media versions for services like OpenURL, library catalogues, search engines or knowledge bases.

### Register

The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register (International Serials Data System), otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items.[12] The Register is not freely available for interrogation on the web, but is available by subscription.

• The print version of a serial typically will include the ISSN code as part of the publication information.
• Most serial websites contain ISSN code information.
• Derivative lists of publications will often contain ISSN codes; these can be found through on-line searches with the ISSN code itself or serial title.
• WorldCat permits searching its catalog by ISSN, by entering "issn:" before the code in the query field. One can also go directly to an ISSN's record by appending it to "http://www.worldcat.org/ISSN/", e.g. http://www.worldcat.org/ISSN/1021-9749. This does not query the ISSN Register itself, but rather shows whether any Worldcat library holds an item with the given ISSN.

## Comparison with other identifiers

ISSN and ISBN codes are similar in concept, where ISBNs are assigned to individual books. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change.

### Extensions

Since the ISSN applies to an entire serial a new identifier, other identifiers have been built on top of it to allow references to specific volumes, articles, or other identifiable components (like the table of contents): the Publisher Item Identifier (PII) and the Serial Item and Contribution Identifier (SICI).

### Media versus content

Separate ISSNs are needed for serials in different media (except reproduction microforms). Thus, the print and electronic media versions of a serial need separate ISSNs,[13] and CD-ROM versions and web versions require different ISSNs. However, the same ISSN can be used for different file formats (e.g. PDF and HTML) of the same online serial.

This "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, and the Web, it makes sense to consider only content, independent of media. This "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier (DOI), an ISSN-independent initiative, consolidated in the 2000s.

Only later, in 2007, ISSN-L was defined in the new ISSN standard (ISO 3297:2007) as an "ISSN designated by the ISSN Network to enable collocation or versions of a continuing resource linking among the different media".[14]

## Use in URNs

An ISSN can be encoded as a uniform resource name (URN) by prefixing it with "urn:ISSN:".[15] For example, Rail could be referred to as "urn:ISSN:0953-4563". URN namespaces are case-sensitive, and the ISSN namespace is all caps.[16] If the checksum digit is "X" then it is always encoded in uppercase in a URN.

### Problems

The URNs are content-oriented, but ISSN is media-oriented:

• ISSN is not unique when the concept is "a journal is a set of contents, generally copyrighted content": the same journal (same contents and same copyrights) may have two or more ISSN codes. A URN needs to point to "unique content" (a "unique journal" as a "set of contents" reference).
Example: Nature has an ISSN for print, 0028-0836, and another for the same content on the Web, 1476-4687; only the oldest (0028-0836) is used as a unique identifier. As the ISSN is not unique, the U.S. National Library of Medicine needed to create, prior to 2007, the NLM Unique ID (JID).[17]
Example: the DOI name "10.1038/nature13777" can be represented as an HTTP string by http://doi.org/10.1038/nature13777, and is redirected (resolved) to the current article's page; but there is no ISSN online service, like http://dx.issn.org/, to resolve the ISSN of the journal (in this sample 1476-4687).

A unique URN for serials simplifies the search, recovery and delivery of data for various services including, in particular, search systems and knowledge databases.[14] ISSN-L (see Linking ISSN above) was created to fill this gap.

## Media category labels

The two standard categories of media in which serials are most available are print and electronic. In metadata contexts (e.g., JATS), these may have standard labels.

### Print ISSN

p-ISSN is a standard label for "Print ISSN", the ISSN for the print media (paper) version of a serial. Usually it is the "default media" and so the "default ISSN".

### Electronic ISSN

e-ISSN (or eISSN) is a standard label for "Electronic ISSN", the ISSN for the electronic media (online) version of a serial.[18]

## References

1. ^ a b "What is an ISSN?". Paris: ISSN International Centre. Retrieved 13 July 2014.
2. ^ "Collection Metadata Standards". British Library. Retrieved 14 July 2014.
3. ^ "ISSN, a Standardised Code". Paris: ISSN International Centre. Retrieved 13 July 2014.
4. ^ ISSN InterNational Centre. "The ISSN for electronic media". ISSN. Retrieved 3 April 2020.
5. ^ "3". ISSN Manual (PDF). Paris: ISSN International Centre. January 2015. pp. 14, 16, 55–58. HTML version available at www.issn.org
6. ^ Example of database implementation where seven-digit integers are used to store ISSNs.
7. ^ Thren, Slawek Rozenfeld. "Using The ISSN (International Serial Standard Number) as URN (Uniform Resource Names) within an ISSN-URN Namespace". tools.ietf.org.
8. ^
9. ^ "Online ISSN Validator". Journal Seeker. Retrieved 9 August 2014.
10. ^ Identification with the GTIN 13 barcode. ISSN International Centre. Archived from the original on 29 June 2020.
11. ^ Kansalliskirjasto, Nationalbiblioteket, The National Library of Finland. "Kansalliskirjasto, Nationalbiblioteket, The National Library of Finland". nationallibrary.fi.CS1 maint: multiple names: authors list (link)
12. ^ "Total number of records in the ISSN Register" (PDF). ISSN International Centre. February 2017. Retrieved 23 February 2017.
13. ^ "ISSN for Electronic Serials". U.S. ISSN Center, Library of Congress. 19 February 2010. Retrieved 12 July 2014.
14. ^ a b "The ISSN-L for publications on multiple media". ISSN International Centre. Retrieved 12 July 2014.
15. ^ Rozenfeld, Slawek (January 2001). "Using The ISSN (International Serial Standard Number) as URN (Uniform Resource Names) within an ISSN-URN Namespace". IETF Tools. RFC 3044. Retrieved 15 July 2014.
16. ^ Powell, Andy; Johnston, Pete; Campbell, Lorna; Barker, Phil (21 June 2006). "Guidelines for using resource identifiers in Dublin Core metadata §4.5 ISSN". Dublin Core Architecture Wiki. Archived from the original on 13 May 2012.
17. ^ "MEDLINE/PubMed Data Element (Field) Descriptions". U.S. National Library of Medicine. 7 May 2014. Retrieved 19 July 2014.
18. ^ "La nueva Norma ISSN facilita la vida de la comunidad de las publicaciones en serie", A. Roucolle. "Archived copy". Archived from the original on 10 December 2014. Retrieved 29 October 2014.CS1 maint: archived copy as title (link)
19. ^ "Road in a nutshell". Road.issn.org. Archived from the original on 5 September 2017. Retrieved 12 September 2017.