[bksvol-discuss] Change to ISBN checking

From: Carrie Karnos <ckarnos@xxxxxxxxx>
To: Bookshare Vol Group <bksvol-discuss@xxxxxxxxxxxxx>
Date: Thu, 17 Sep 2009 15:20:16 -0700 (PDT)
Hi gang,

Engineering has just deployed a new version of the system, that has a change to 
ISBNs. In the past, the only check that they made was to make sure that the 
length of the ISBN was correct. Now they are also doing a checksum validation 
on all ISBNs. While software engineers know what checksums are, I expect that 
most people don't. It's basically a method to make sure you haven't entered a 
bad ISBN, flipped 2 of its digits, etc. If you're curious, I have included the 
introduction of an article from Wikipedia about checksums at the end of this 
email.
Bottom line is that if you put in an ISBN number and get an error, please 
double-check the ISBN number that you entered and fix any mistakes. If you're 
positive that you've entered the correct number and still get an error, please 
don't enter anything in the ISBN field, click on Continue, and fill out the 
metadata of the book yourself.

Thanks! Carrie


Here is the introduction to the Wikipedia article 
(http://en.wikipedia.org/wiki/Checksum). (By the way, not only do ISBNs have 
checksums but also credit cards, bank account numbers, etc.)



A checksum or hash sum is a fixed-size datum computed from an arbitrary block 
of digital data for the purpose of detecting accidental errors that may have 
been introduced during its transmission or storage. The integrity of the data 
can be checked at any later time by recomputing the checksum and comparing it 
with the
stored one. If the checksums do not match, the data was certainly
altered (either intentionally or unintentionally).
The procedure that yields the checksum from the data is called a checksum 
function or checksum algorithm.
A good checksum algorithm will yield a different result with high
probability when the data is accidentally corrupted; if the checksums
match, the data is very likely to be free of accidental errors.
Checksum functions are related to hash functions, fingerprints, randomization 
functions, and cryptographic hash functions. However, each of those concepts 
has different applications and therefore different design goals. Check digits 
and parity bits are special cases of checksums, appropriate for small blocks of 
data (such as Social Security numbers, bank account numbers, computer words, 
single bytes, etc.). Some error-correcting codes are based on special checksums 
that not only detect common errors but
also allow the original data to be recovered in certain cases.
[bksvol-discuss] Change to ISBN checking

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