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Working with ISBNs


IDII Note: This is a very good and educational article on ISBN barcoding basics. Understanding the code that is utilized for a barcode is important. We hope this article helps you. IDII thanks Data Technology Software Integration Ltd for the permission to use this white paper. This article appeared in Material Management and Distribution magazine.


MM&D - Working with ISBNs The publishing industry was perhaps the first to organize an industry-wide numbering system. Almost every book carries an ISBN number, and many catalogs, such as 'Books in Print' are cross-referenced by this invaluable identifier.

Most books are barcoded. Publisher compliance to the EAN-13 symbology is almost total. Children's books and specialty products cause some problems, but the overall standard of barcoding conformance is the envy of other industries.

This combination of industry-wide agreement on item identification and almost universal compliance to barcode standards makes book handling an ideal candidate for automated warehouse systems.

However, distributors are often dismayed to discover that they can't easily scan a book jacket and extract the ISBN. This article explains why, and what you can do about it.

About ISBNs

An ISBN is a 10-character string. The leftmost character is a 'Hemisphere' number, and the rightmost is a checkdigit. The middle eight digits are divided to identify the publisher and uniquely identify a title from that publisher.

This description could almost exactly be used to describe a 12-digit UPC or 13-digit EAN code. However, there are two significant differences:

  • The number of digits assigned to the publisher are not fixed. A major publisher might be assigned a valuable two-digit number, reserving six digits for his catalog of titles. A tiny publisher might be assigned a six-digit number, with only room for a few titles. It is customary to separate these fields with a dash in the human-readable version.

  • The checkdigit is calculated MOD-11, which means that it may contain the alpha character 'X' in addition to the numeric digits. An ISBN cannot be stored as a number since it may be alphanumeric.

Bookland EAN

When retail barcodes started to become ubiquitous, the publishers wisely decided not to create their own symbology. They approached the EAN organization, and cut a deal to map their ISBN numbers onto the EAN-13 barcode standards.

EAN codes are administered on a national or territorial basis by 'Numbering Organizations'. Since the publishers already had an international organization, they were granted a fictitious country, 'Bookland', and control over their numbers.

All 'Bookland EANs' start with 978 prefix. The usual nine digits that represent the company and item numbers are mapped from the first nine digits of the ISBN. The difficulty is that the checkdigit is recalculated according to the EAN standards. The tenth ISBN digit simply disappears.

The significance is that the ISBN cannot be scanned out of the EAN barcode. By discarding the EAN prefix, you may extract the first nine digits, but then you must recalculate the ISBN checkdigit yourself.

Mass Market Books

If you look at the back of a hardback or trade paperback, you will see the human-readable ISBN and, below it, an EAN-13 barcode with another human-readable number.

However, mass-market paperbacks often have a UPC on the back. Usually the price is embedded in this UPC, either in the right-most UPC digits or in the supplemental barcode. Use of price-point barcodes mean that the UPC cannot generally be used to identify the book.

Some books have both UPC and Bookland EAN barcodes on the back. You may have to check the inside front cover to find the Bookland EAN. If you are automating your warehouse, you will have to train your staff to only scan the barcode that starts with '978'.

Converting to ISBN

Some high-end retail scanning equipment will automatically convert a Bookland EAN into an ISBN, but RF systems and simple wedge scanners require you to implement the conversion in software.

The algorithm is simple, and can be implemented in about four lines of BASIC programming. Here's how to recalculate manually:

Start with a 13-digit EAN barcode, drop the 978 prefix, and save the next nine digits. You can throw away the final digit - it's just the EAN checkdigit.

With your nine-digit number, multiply the first digit of the code by 10, the second digit by 9, the third digit by 8, and so on, adding the results together (a 'sum of products').

Take the modulus-11 by dividing the resulting sum-of-products by 11 and keeping only the remainder. For example, if the sum-of-products is 174, then taking modulus-11 leaves a remainder of 9 (hint: 15 times 11 is 165). The remainder will always be between 0 and 10.

Finally, subtract your remainder from 11. If you end up with 11, use '0', if you end up with 10, use 'X', otherwise use whatever you got, glue it to the end of your nine digits, and voila: an ISBN!

As well as being useful in the supply chain, this algorithm makes an interesting math exercise for your child prodigy.

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