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**ISSN Code Format and Structure**:
– An ISSN is an eight-digit code divided by a hyphen into two four-digit numbers.
– The last digit is a check digit, making the ISSN unique with its first seven digits.
– The structure is expressed as NNNN-NNNC with the check digit being 0-9 or X.
– It can be represented by a regular expression: ^[0-9]{4}-[0-9]{3}[0-9X]$

**EAN Encoding and Usage**:
– ISSNs can be encoded in EAN-13 barcodes with a 977 country code.
– EAN-13 includes 7 main digits of the ISSN and 2 publisher-defined digits.
– The EAN check digit may not match the ISSN check digit.
– EANs provide a way to include ISSN information in barcodes.

**ISSN Administration and Usage**:
ISSN codes are assigned by ISSN National Centres coordinated by the ISSN International Centre.
– The International Centre, established in 1974, is based in Paris and is a collaboration between UNESCO and the French government.
ISSN codes are crucial for ordering, cataloging, and interlibrary loans.
– The system distinguishes between print ISSN (p-ISSN) and electronic ISSN (e-ISSN).

**ISSN-L and Register**:
– ISSN-L is a unique identifier for all versions of a serial across different media, facilitating linking among different versions.
– The ISSN Register contains records for assigned ISSNs worldwide, with over 1.9 million items by the end of 2016.
– ISSN-L simplifies search, retrieval, and delivery across all media versions.
ISSN codes are typically included in the print version of serials.

**URN Encoding and Challenges**:
– An ISSN can be encoded as a URN by prefixing it with ‘urn:ISSN:’.
– URN namespaces are case-sensitive, with the ISSN namespace in all caps.
– Challenges include non-uniqueness of ISSN, lack of resolution mechanisms like DOI, and the creation of NLM Unique ID and ISSN-L to address these issues.

ISSN (Wikipedia)

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

International Standard Serial Number
OrganisationISSN International Centre
Introduced1976; 48 years ago (1976)
No. issued> 2,500,000
No. of digits8
Check digitWeighted sum
ISSN encoded in an EAN-13 barcode with sequence variant 0 and issue number 05
Example of an ISSN, 2049-3630, encoded in an EAN-13 bar code, with explanation
ISSN 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

The ISSN system was first drafted as an International Organization for Standardization (ISO) international standard in 1971 and published as ISO 3297 in 1975. 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). 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.

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