Numéros ISBN

The ISBN began as a warehouse problem. In 1965 the British bookseller WHSmith announced that it would computerise its stock control and needed a standard number for every book it carried. Gordon Foster, later emeritus professor of statistics at Trinity College Dublin, designed the nine-digit Standard Book Number that came out of that work. David Whitaker turned the SBN into a working national system in the United Kingdom in 1967 and is generally called the father of the ISBN; Emery Koltay arrived at the same idea independently in the United States in 1968 and went on to direct the American ISBN agency at R. R. Bowker. ISO took the scheme up and published the ten-digit ISBN as ISO 2108 in 1970. Converting an old SBN was a matter of writing a zero in front of it.

The ten-digit form used a mod-11 check digit, which is why some ISBNs end in X. Eleven possible remainders need eleven symbols, and there are only ten digits, so X stands in for ten — and only ever in the final position.

By the 1990s the ISBN was both running short of numbers and sitting awkwardly beside retail. Supermarkets scanned thirteen-digit EAN barcodes; bookshops scanned ten-digit ISBNs. The fix was Bookland, an invented country handed the EAN prefix 978 so that a book could be numbered like any other retail article. From 1 January 2007 the ISBN itself became thirteen digits — the old number with 978 in front and a fresh mod-10 check digit — completing a migration that had opened on 1 January 2005. A second Bookland prefix, 979, was made available to extend capacity. Inside it, 979-0 is set aside for International Standard Music Numbers, so sheet music and books share one numbering space without ever colliding.

Propriétés principales

• An ISBN-13 is thirteen digits: a three-digit GS1 prefix (978 or 979), a registration group element, a registrant element, a publication element and one check digit.
• The ISBN-10 check digit is whatever makes the sum of all ten digits, weighted 10, 9, 8 … 1 from the left, a multiple of 11. The remainder can be 10, so X is used for that case and appears only in the last position.
• The ISBN-13 check digit makes the sum of all thirteen digits, weighted alternately 1 and 3 starting from the left, a multiple of 10.
• Every 978-prefixed ISBN-13 has an exact ten-digit equivalent: drop the 978 and recompute the check digit under the mod-11 rule. A 979-prefixed ISBN has no ten-digit form at all.
• The mod-11 rule catches every single mistyped digit and every transposition of two adjacent digits. The mod-10 rule used by ISBN-13 is weaker: swapping adjacent digits that differ by 5 — a 1 and a 6, say — leaves the check digit unchanged, because the sum shifts by twice the difference.
• Under prefix 978, registration groups 0 and 1 are English-language areas, 2 is French, 3 German, 4 Japan, 5 the former USSR and 7 China. Group 6 exists only as longer multi-digit prefixes.
• Registration group 979-0 is reserved for International Standard Music Numbers (ISO 10957), which have begun with that prefix since 1 January 2008. Before then an ISMN was written with a leading letter M.
• Hyphen positions are not decorative: they mark the registration group and registrant boundaries, whose lengths are published in the International ISBN Agency range message rather than derivable from the digits.

Où on les rencontre

• Printed above the barcode on the back cover of almost every commercially published book — an ISBN-13 under the 978 or 979 prefix is a valid EAN-13, so a bookshop and a supermarket can use the same scanner.
• Library and union catalogues such as WorldCat use the ISBN as a matching key when merging records that arrived from different cataloguing sources.
• Bibliographic metadata standards carry it as the primary product identifier for a book: MARC 21 field 020 and the ONIX for Books message both have a dedicated place for it.
• Amazon keys book listings on the ISBN; for books with a ten-digit ISBN the ASIN has historically been that number itself.
• Open Library and Google Books expose ISBN-keyed lookup endpoints, which is how an app resolves a scanned barcode into a title and author.