ISBN Book Code

The ISBN (for International Standard Book Number) is an identifier attributed to each published book used to define it at the international level (title, edition, author, publisher) which is practical for both readers and libraries.

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ISBNs originally included 10 digits (hence its name ISBN 10) and in January 2007 the length of the ISBN was extended to 13 digits.

ISBN 13 is actually made of the number ISBN 10 with 3 new digits positioned at the beginning (978 ou 979) and a new control checksum.

The two numbers are generally coded on barcodes with the EAN standard, respectively EAN-10 and EAN-13.

An ISBN code is composed of four segments A - B - C - D.

A is a geographical area code of variable length (up to 5 characters).

B is a variable length code editor (up to 7 characters)

C is the book code (usually sequential). This code is completed with leading zeros if necessary.

D is the code checksum (verification key) 1 character

The abbreviation ISBN stands for International Standard Book Number

An ISBN is used to identify books, while an ISSN (International Standard Serial Number) is used to identify serial publications, such as journals, magazines and newspapers.

An ISBN is specific to books, while a DOI (Digital Object Identifier) is a unique identifier used for digital resources, such as research articles, online documents, and other web content.

No, not all books necessarily have an ISBN. Some self-published or very old books may not have one.

The algorithm for implementing an ISBN 10 checksum is // Pseudo-code
function calculateISBN10Checksum(ISBN) {
total = 0
for (i = 0; i < 9; i++) {
total += ISBN[i] * (10 - i)
}
checksum = (11 - (total % 11)) % 11;
if (checksum == 10) checksum = "X"
return checksum
}

The algorithm for implementing an ISBN 13 checksum is // Pseudo-code
function calculateISBN13Checksum(ISBN) {
total = 0
for (i = 0; i < 12; i+=2) {
total += ISBN[i] + (ISBN[i+1] * 3)
}
checksum = (10 - total % 10) % 10
return checksum
}

The presence of an X at the end of an ISBN code is due to the method of calculating the checksum. For ISBN 10, the last digit is the check digit, it is calculated using a formula which involves a weighted sum of the first nine digits of the ISBN modulo 11. When this sum is equal to 10, instead of representing this number by the 2 digits 10, it was decided to use X to remain at 10 characters in the ISBN.