check digit ?

Posted on 2007-10-04
Medium Priority
Last Modified: 2008-01-09

I need to check wether an Isin code specified by a user is valid or not..
I found this article exaplaining an algoryhtm to compute a "check digit" : http://en.wikipedia.org/wiki/International_Securities_Identifying_Number
But what do I have to do after calculating this check digit ?

Maybe if you have some experience in security, you understand what this is about ? (I have none)

Thank you.
Question by:matthew016
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LVL 59

Accepted Solution

Chris Bottomley earned 2000 total points
ID: 20013017
Check digits are often used to support validation of a data sequence which is how it appears to b eused in this instance.

i.e. if you enter the ISIN but make a typo the check digit will likely indicate the fact and you can prompt for a re-entry.  It means when entering an ISIN for validation you should calculate the correct check digit and ensure the data as entered validates against it.


Author Comment

ID: 20013110
I am not sure I understand.
If user makes a typo, I will compute a certain digit. How can I detect from this digit that he made a typo ?
LVL 59

Expert Comment

by:Chris Bottomley
ID: 20013180
Error checking is a speciality in it's own right ... i'm not saying i'm an expert but as far as I can see the referenced syntax will indicate an error exists but it is not error correcting and will not indicate which character, (or characters are wrong).

i.e. when requesting or receiving the data you should calculate the check digit for each datum and ensure it is correct before proceeding and where any individual datum is wrong reject it and move on.


Author Comment

ID: 20013203
Well I need to know how I detect an error exists.
I do not want to correct the error.

But now I am maybe confusing
* error detection in some kind of I/O operations, etc. and
* validation to check if the data entered is a valid sequence

Author Comment

ID: 20013216
nevermind ...

I see that I can check the digit computed with the last number of the sequence number.

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