Introduction and Code Format - An ISSN is an eight-digit serial number used to uniquely identify a serial publication. - It helps distinguish between serials with the same title. - ISSNs are used in ordering, cataloging, and interlibrary loans. - The ISSN system was first drafted as an ISO international standard in 1971. - ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard. - An ISSN is an eight-digit code, divided by a hyphen into two four-digit numbers. - The last digit is a check digit, uniquely representing the ISSN. - The general form of the ISSN can be expressed as NNNN-NNNC. - The check digit is calculated using a specific algorithm. - The ISSN can be confirmed using an online ISSN checker.

Use in EANs - ISSNs can be encoded in EAN-13 bar codes with a 977 country code. - The main digits of the ISSN are included, followed by 2 publisher-defined digits. - The EAN check digit may not match the ISSN check digit.

Code Assignment and Maintenance - ISSN codes are assigned by ISSN National Centres coordinated by the ISSN International Centre. - The International Centre is an intergovernmental organization created in 1974. - The ISSN Register contains records for over 1,943,572 items. - The Register is not freely available but can be accessed by subscription. - ISSN codes are typically included in the print version of a serial and on serial websites.

Comparison with Other Identifiers - ISSN and ISBN codes are similar in concept. - ISBNs are assigned to individual books, while ISSNs are for serials. - An ISSN is an anonymous identifier associated with a serial title. - A new ISSN is assigned when a serial undergoes a major title change. - Extensions like PII and SICI allow references to specific components of a serial.

Use in URNs and Problems - An ISSN can be encoded as a URN by prefixing it with 'urn:ISSN:'. - URN namespaces are case-sensitive, and the ISSN namespace is all caps. - If the checksum digit is X, it is always encoded in uppercase in a URN. - URNs need to point to unique content, unlike ISSN which may have multiple codes for the same journal. - ISSN is not unique when the concept of a journal is a set of contents. - The same journal may have two or more ISSN codes. - The U.S. National Library of Medicine created the NLM Unique ID (JID) to address this issue. - ISSN does not offer resolution mechanisms like DOI or URN. - DOI is often used as a URN for articles.

Additional Group: Media category labels - Two standard categories of media for serials: print and electronic. - These categories may have standard labels in metadata contexts. - Print ISSN (p-ISSN) is the ISSN for the print media version of a serial. - Electronic ISSN (e-ISSN or eISSN) is the ISSN for the electronic media version of a serial.

Additional Group: ROAD - ROAD: Directory of Open Access Scholarly Resources. - Produced by the ISSN International Centre and UNESCO. - Helps simplify the search, recovery, and delivery of data for various services. - Particularly useful for search systems and knowledge databases. - ISSN-L (Linking ISSN) was created to provide a unique URN for serials.

Additional Group: See also - CODEN. - WorldCat (ISSN-resolve service). - References for further information on ISSN.