# International Standard Serial Number

ISSN encoded in an EAN-13 barcode with sequence variant 0 and issue number 5.
Example of an ISSN encoded in an EAN-13 barcode with explanation.
ISSN expanded with sequence variant 0 to a GTIN-13 and encoded in an EAN-13 barcode with and EAN-2 add-on designating issue number 13.

An International Standard Serial Number (ISSN) is a unique eight-digit number used to identify a periodical publication at a specific media type.[1] It is internationally accepted as a fundamental identifier for distinguishing between identical serial titles and facilitating checking and ordering procedures, collection management, legal deposit, interlibrary loans etc.[2]

When a periodical is published, with same content, in two or more different media, a different ISSN is assigned to each media type — in particular the print and electronic media types, named print ISSN (p-ISSN) and electronic ISSN (e-ISSN or eISSN).

The ISSN system was first drafted as an ISO international standard in 1971 and published as ISO 3297 in 1975.[3] The ISO subcommittee TC 46/SC 9 is responsible for the standard. To assign a unique identifier to the serial as content (linking among the different media), ISSN-L must be used, as difined by ISO 3297:2007.

## Code format

The format of the ISSN is an eight digit number, divided by a hyphen into two four-digit numbers.[1] The last digit, which may be 0-9 or an X, is a check digit. The general form of the ISSN code can be expressed by a PCRE regular expression,

 \d{4}-\d{3}[\dX]


The ISSN of the journal Hearing Research, for example, is 0378-5955, the check digit is 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:
$0\cdot 8 + 3\cdot 7 + 7\cdot 6 + 8\cdot 5 + 5\cdot 4 + 9\cdot 3 + 5\cdot 2$
$= 0 + 21 + 42 + 40 + 20 + 27 + 10$
$= 160$.
The modulus 11 of this sum is then calculated: divide the sum by 11 and determine the remainder.
$\frac{160}{11} = 14\mbox{ remainder }6=14+\frac{6}{11}$.
If there is no remainder the check digit is 0, otherwise the remainder value is subtracted from 11 to give the check digit:
$11 - 6 = 5$
5 is the check digit.
An upper case X in the check digit position indicates a check digit of 10 (so it is 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.

Also, there is an Online ISSN checker can check validity of ISSN base on above algorithm.[4]

## Code assignment

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. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register (International Serials Data System) otherwise known as the ISSN Register. As of 2011, the ISSN Register contained records for 1,623,566 items.[5]

## 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 periodical, in addition to the ISSN code for the periodical as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a periodical title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a periodical each time it undergoes a major title change.

Since the ISSN applies to an entire periodical a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components (like the table of contents).

### Media vs Content

Separate ISSN are needed for serials in different media (with the exception of reproduction microforms). Thus the print and electronic media versions of a serial need separate ISSN.[6] Also, a CD-ROM version and a web version of a serial require different ISSN since two different media are involved. However, the same ISSN can be used for different file formats (ex. PDF and HTML) of the same online serial.

This "media-oriented identification" of serials make sense in the 1970's. In the 1990's, with the PCs, good screens, and the Web, what make sense is to consider only content, independent of media. "Content-oriented identification" of serial's contents, arrives with the indecs Content Model and its application the Digital Object Identifier (DOI).

ISSN not updated, but 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”.[7]

## Availability

The ISSN Register is not freely available for interrogation on the web but is available by subscription. There are several routes to the identification and verification of ISSN codes for the general public.

• the print version of a periodical typically will include the ISSN code as part of the publication information
• most periodical 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 periodical title
• WorldCat permits searching their catalog by ISSN by entering "issn:"+ISSN 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.

## Use in URNs

An ISSN can be encoded as a Uniform Resource Name (URN) by prefixing it with "urn:ISSN:".[8] For example Rail could be referred to as "urn:ISSN:1534-0481". URN namespaces are case-sensitive, and the ISSN namespace is all caps.[9] If the checksum digit is "X" then it is always encoded in uppercase in a URN.

### Problems

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

• ISSN is not unique when the concept is "journal is a set of contents, generally copyrighted content": the same journal (same contents and same copyrighs) have 2 or more ISSN codes. A URN need to point to "unique content" (a "unique journal" as a "set of contents" reference).
Examples: Nature have an ISSN for print, 0028-0836, and another for the same content at Web, 1476-4687; only the oldest (0028-0836) is used as unique identifier. As ISSN is not unique, NLM need to createm, prior to 2007, the JID.
• ISSN not offer resolution mechanisms, as Digital Object Identifier (DOI), so, the DOI is used as URN for articles, with (by historical reasons) no need of ISSN existence.

An unique URN for serials simplifies the search, recovery and delivery of data for various services including, in particular, search systems and knowledge databases.[7] ISSN-L was created to fill this gap.

## ISSN variants

### print ISSN

The "default" ISSN. ISSN for print media (paper) version of the periodic.

### electronic ISSN

ISSN for electronic media (online) version of the periodic.