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Gender isn't exactly part of your primary key. You're not going to have somehow read-only'd it.

That depends on where you live. In Denmark we all have a 10-digit "CPR-number" and it is used pretty much everywhere as a primary key. It contains your birthday (in DDMMYY-format), followed by a 3-digit serial number and finally a single "checksum" digit (*). CPR-numbers with an even checksum digit is given to females, while the odd checksums are given to males. So our gender is part of our primary key and we do get a new CPR-number, if we get a sex-change.

*: The description above is how it used to be. The old format only allowed about 500 CPR-numbers per date and in some cases, when the correct birthday was unknown, people have been given the fictive birthday January 1st 1965 or 1966. Unfortunately that resulted in an overflow of CPR-numbers for those two dates, so in 2007 it was decided to use a random number as the final digit in those (so far 18) cases. As far as I know, the random digit still has to be odd for males.

We have that register here in Denmark, it is regulated by the Danish Act on the Civil Registration System.

http://cpr.dk/Index/dokumenter.asp?o=7&n=0&h=7&t=1 &d=140&s=5

"Section 1. The purpose of the Act is to ensure that

      1. anyone covered by s 3(1), has a civil registry number,
      2. the Civil Registration System (CPR) contains basic personal data about anyone who has a civil registry number,
      3. everyone is nationally registered at the address at which they are actually living or staying, and
      4. the information in CPR can be conveyed expediently to public authorities and private individuals with a justified interest in the same. "

Not quite. It's described here.

Basically, each digit is multiplied with the corresponding weight. So the first digit is multipled by 4, the next by 3, and so on.

You then add up all these products. This sum is divided by 11. The control digit is given by subtracting the remainder from 11.

Suppose your CPR number is 123456-789, and we need the control digit. First we multiply:

1*4 + 2*3 + 3*2 + 4*7 + 5*6 + 6*5 + 7*4 + 8*3 + 9*2
= 174
174 / 11 = 15 remainder 9
11 - 9 = 2, so the full CPR number is:
123456-7892.

If the remainder turns out to be 1, then the control digit would have been 10; in this case, the CPR number is discarded. (In the ISBN system you use the letter X to represent a control digit of 10.)

Actually, it is Y2K compliant. Digits 7 and 8 indicate a batch number, which changes every 3 decades or so. With a special table available from the CPR website you can decode the exact year.

Our CPR (Central Person Registry) stores your CPR-number. Mine looks like this:

130477-1235 (no, this is not my real CPR-number)

This indicates that my birthdate is the 13th day of the 04th month of the 77th year.

1235 is the "checksum" and gender-marker; even numbers for women, uneven for men. I think they use X for women and Y for men without a permanet citizen ship (refugees and the like).

Also, the entire number has to pass some kind of test, but I can't remember how it's used.

The CPR also has the current address of each person along with an opt out feature for commercial mail targeted at you, which is nice, because all companies in Denmark have to comply by that setting, but they only have access to the address through CPR.

You can read a lot more about the system here.

I am a proponent of personal privacy, and I don't have a problem with this system - probably because I can't think of a single intrusion into my privacy caused by it.

I think it comes down to "trust", and so far I haven't had a reason not to trust the CPR.

They should be based in some small european country - maybe Denmark or Sweden as there is a clear message from goverment about spam-mail (it will be made illigal in the next couple of years)

Spam is illegal in Denmark as of 1st July 2000. If you can read Danish, please see this page. Basically what you do is to let the Danish Central Person Register put your name on the so-called ``Robinson List'' (a derogative term coined by marketroids who claim that you are living on a desolate island if you do not wish to receive commercial ads). Once your name is on that list, commercial entities are no longer allowed to send you unsolicited commercial junk via snailmail, e-mail or fax, nor may they contact you on your phone.

Suprisingly enough, since 1st July this year only about 3,000 Danes have opted to have their name put on this anti-spam list, whereas almost 200,000 people have decided to register on a send-more-spam list maintained by the Danish postal corp. Go figure...

// Klaus
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